The mistakes GRE subject-test questions are built to catch.

The quantity was rescaled by the raw factor even though the physical law raises that factor to a power or takes its root.

Write the law as a power relation first, then apply the change to that power rather than to the quantity itself. Halving a radius rarely halves anything.

134 wrong answers written to catch it, 57 of them in classical mechanics · wrong method

The physics is right but the final ratio was inverted, so the answer is one over the value the prompt requested.

Read the ratio in the order the prompt states it, and check the answer falls on the side of one you expect.

96 wrong answers written to catch it, 25 of them in classical mechanics · calculation or execution error

The selected outcome does not conserve the quantity that is conserved under the stated conditions.

List the quantities that are conserved under the stated conditions, then discard every option that breaks one. This eliminates faster than computing does.

33 wrong answers written to catch it, 15 of them in classical mechanics · concept gap

The chosen answer ignores how far the mass lies from the rotation axis, which is what sets the moment of inertia.

Ask where the mass sits relative to the axis. Rotation is governed by distance squared, so moving mass outward matters more than adding it near the centre.

11 wrong answers written to catch it · concept gap

The magnitude is handled but the direction that a cross product fixes was taken along the wrong axis or sign.

Redo the right-hand rule with the vectors in the order the definition gives them, then check the sign of the result against a case you already know.

16 wrong answers written to catch it · concept gap

The chosen direction is that of the electric or magnetic field rather than the propagation direction they jointly define.

Take the two field directions first. The wave travels along the direction their cross product defines, which is neither of them.

9 wrong answers written to catch it · concept gap

The chosen answer scales a quantity that the described change does not touch, which is the mirror image of ignoring a real dependence.

List what the described change actually touches and hold everything else fixed. Scaling a quantity the setup never altered is as wrong as ignoring one it did.

11 wrong answers written to catch it, 6 of them in electromagnetism · concept gap

The sine factor in a magnetic force law was evaluated as though the angle between the vectors were different.

Identify which two vectors the angle sits between, and evaluate the sine factor from that angle alone. The angle to a third direction is not the one in the law.

9 wrong answers written to catch it, 6 of them in electromagnetism · wrong method

The combination rule for the other wiring topology was used for this circuit.

Decide series or parallel from what the current is free to do, not from how the diagram happens to be drawn on the page.

8 wrong answers written to catch it, 6 of them in electromagnetism · wrong method

The chosen answer tracks how large a quantity is when the law depends on how fast that quantity is changing.

Ask whether the law depends on how large the quantity is or on how fast it is changing, and read the graph or the description for that one thing.

8 wrong answers written to catch it, 5 of them in electromagnetism · concept gap

The counting rule for allowed quantum numbers, degenerate states, nodes, or active degrees of freedom was applied incorrectly.

Rebuild the count from the rule that generates the states — allowed quantum numbers, nodes, active degrees of freedom — instead of recalling a total.

78 wrong answers written to catch it, 34 of them in quantum mechanics · concept gap

A real effect was taken to an extreme the stated conditions never reach.

Work out how far the stated conditions actually push the effect before you treat it as an extreme. Real effects have sizes, and most of them are small here.

109 wrong answers written to catch it, 22 of them in quantum mechanics · concept gap

The chosen answer makes intensity change a per-photon property that only frequency controls.

Separate how many photons arrive from how much energy each one carries. Brightness changes the first; only frequency changes the second.

2 wrong answers written to catch it · concept gap

The formula and the substituted givens are right; the number that came out of the division, multiplication, or rounding is not.

Re-run the final arithmetic once with rounded numbers and check the order of magnitude. This catches the slip without costing a second full calculation.

211 wrong answers written to catch it, 53 of them in thermodynamics · calculation or execution error

The chosen answer moves heat or entropy in a direction that is forbidden without work input.

Check the direction of heat flow and the sign of the entropy change before accepting an outcome. Without work going in, heat does not run uphill.

20 wrong answers written to catch it · concept gap

A gas or radiation law that is written in absolute temperature was evaluated with a Celsius value, so the ratio comes out wrong.

Convert every temperature to kelvin before it enters a law written in absolute temperature. A ratio of Celsius readings is not a ratio of temperatures.

4 wrong answers written to catch it · wrong method

The number quoted belongs to another cubic lattice type than the one named in the prompt.

Name the lattice in the prompt and recount its atoms per cell for that lattice. The three cubic cells give three different counts, and they are easy to blur together.

11 wrong answers written to catch it · concept gap

Relative speeds were combined by ordinary addition or subtraction instead of the relativistic rule, which can even push the result past c.

Combine relative speeds with the relativistic rule whenever either is a serious fraction of the speed of light, and check that the result stays below it.

18 wrong answers written to catch it · wrong method

The chosen expression is a corrupted variant of the standard formula for this quantity: a real formula, but not the one this situation calls for.

Rederive the formula from a case you can check rather than recalling it under time pressure. A near-miss variant looks exactly as convincing as the real one.

61 wrong answers written to catch it, 28 of them in calculus · concept gap

A convergence test or comparison was invoked in a direction that gives no conclusion for this series or integral, or was dismissed where it does decide.

Check that the test's hypotheses hold here and that its conclusion answers the question. A test that gives no conclusion is not evidence either way.

40 wrong answers written to catch it, 28 of them in calculus · wrong method

A differentiation or antidifferentiation rule was used where a different one governs this expression.

Name the structure of the expression — product, quotient, composition — before reaching for a rule. The rule follows from the structure, not from what the terms look like.

29 wrong answers written to catch it, 21 of them in calculus · wrong method

The point was substituted into an indeterminate or discontinuous expression and the resulting symbol was reported, instead of resolving the form first.

Resolve the form first — factor, expand, or apply a limit theorem — and substitute only once the expression is defined at the point.

26 wrong answers written to catch it, 20 of them in calculus · wrong method

The odd or even symmetry of the integrand over a symmetric interval was not used, so a cancellation was computed away or invented.

Check whether the integrand is odd or even over a symmetric interval before you integrate anything. Symmetry often replaces the whole calculation.

18 wrong answers written to catch it · concept gap

The chosen expression is what differentiating produces where the problem asks you to antidifferentiate, or the reverse.

Check whether you are being asked to differentiate or to antidifferentiate, then verify by running the opposite operation on your answer.

18 wrong answers written to catch it, 14 of them in calculus · wrong method

The outer rule was carried out correctly, but the derivative of the inner function was never multiplied in — or it was placed inside the outer function instead of alongside it.

Name the inside function explicitly, then multiply by its derivative as a separate factor sitting alongside the outer result.

14 wrong answers written to catch it, 13 of them in calculus · wrong method

The numerator was built correctly but was never divided by the interval length, the squared norm, or the count that the definition divides by.

Finish the definition. The interval length, the squared norm, or the count the formula divides by is part of the answer, not decoration.

22 wrong answers written to catch it, 12 of them in calculus · calculation or execution error

Convergence of the series was taken for convergence of the series of absolute values, or the reverse.

Test the series of absolute values as a separate question before claiming absolute convergence.

9 wrong answers written to catch it, 5 of them in calculus · concept gap

A path-independent integral was treated as depending on the route taken, or a path-dependent one was treated as fixed by the endpoints.

Check whether the field has a potential function. If it does, only the endpoints matter; if it does not, the route is part of the answer.

6 wrong answers written to catch it, 4 of them in calculus · concept gap

Repeated multiplication was replaced by repeated addition, so exponential growth or decay was extrapolated in equal steps.

Count how many times the quantity multiplies rather than how much it adds each step. Compounding and linear change agree only for one step.

4 wrong answers written to catch it · concept gap

A quantity that a change of basis or a structure-preserving map holds fixed was treated as changing, or the reverse.

List what the transformation is allowed to change and what it must preserve, then judge the quantity against that list.

31 wrong answers written to catch it, 21 of them in linear algebra · concept gap

The method is right, but entries or components were read from the wrong places: an off-diagonal for a diagonal, a row for a column, two components swapped, or one entry skipped.

Say which row and which column each number comes from before you use it. Reading the wrong entry is a silent error: the method looks right the whole way through.

24 wrong answers written to catch it, 20 of them in linear algebra · misread condition

The sum and the product of the eigenvalues were interchanged.

Hold on to which one sums the eigenvalues and which one multiplies them, then check which the question wants.

18 wrong answers written to catch it · concept gap

Rank plus nullity was balanced against the target space, or against the number of rows, rather than against the dimension of the domain.

Count the dimension of the domain first. Rank and nullity add up to that, not to the dimension of the space you are mapping into.

14 wrong answers written to catch it · wrong method

The multiplicity of the eigenvalue in the characteristic polynomial was reported instead of the dimension of its eigenspace.

Compute the dimension of the eigenspace separately from the multiplicity of the root, and compare the two. They agree only when the matrix is diagonalisable.

4 wrong answers written to catch it · concept gap

One clause of the definition — closure, inverses, absorption, independence, or a boundary case — was never checked, so an object that fails it was accepted.

Run every clause of the definition, including the clause that looks too obvious to check. That is usually the one the item is built on.

197 wrong answers written to catch it, 60 of them in abstract algebra · concept gap

The size of the group, of a subgroup, or of the index was reported where the order of a single element was asked, or the reverse.

Check whether the question asks for the order of a single element or for the size of the whole group. The two are related but almost never equal.

35 wrong answers written to catch it · concept gap

The order was classified without correctly checking whether it is a power of a single prime.

Factor the order into primes first, then apply the theorem to what the factorisation shows rather than to what the number looks like.

24 wrong answers written to catch it · concept gap

An element was classified as invertible when it is a zero divisor, or the reverse, without checking the coprimality condition that separates them.

Test directly whether the element has an inverse. The coprimality condition is what separates a unit from a zero divisor, and it is quick to check.

24 wrong answers written to catch it, 23 of them in abstract algebra · concept gap

The chosen property is a genuine axiom of the structure, but not the one the term in the prompt picks out.

Name the axiom the term in the prompt actually picks out, then check the structure against that one. Several axioms hold; only one is being tested.

20 wrong answers written to catch it, 10 of them in abstract algebra · concept gap

The chosen answer asserts a condition that is sufficient or simply false here, rather than the one that is actually required.

Ask whether the property is required here or merely enough here. A condition that is enough for the conclusion cannot be used to justify the conclusion in general.

130 wrong answers written to catch it, 45 of them in real analysis · concept gap

The strict or non-strict inequality at the boundary was chosen the wrong way, so the borderline case is misclassified.

Test the boundary point itself and see whether it belongs. Whether the inequality is strict is usually the whole question.

62 wrong answers written to catch it, 28 of them in real analysis · concept gap

The quantifiers were reordered or the implication was reversed, which states a different condition from the definition being tested.

Read the quantifiers in the order they are written and keep the implication pointing the way the definition points. Swapping either states a different claim.

46 wrong answers written to catch it, 20 of them in real analysis · concept gap

The count was made as if the selections were ordered, so each unordered choice was counted more than once.

Decide whether two selections in a different order count as the same outcome before you choose a formula. That single decision picks the formula for you.

16 wrong answers written to catch it · wrong method

An uncountable set was treated as countable (or the reverse), so the cardinality comparison fails.

Ask whether the set can be listed by a rule. An explicit listing or a diagonal argument settles it; intuition about size does not.

17 wrong answers written to catch it, 8 of them in real analysis · concept gap

A bound that depends on the point was treated as a bound that works for the whole interval at once, or the reverse.

Ask whether one bound works at every point at once, or whether the bound you found still depends on the point you picked.

10 wrong answers written to catch it, 6 of them in real analysis · concept gap

The sign of the derivative at the equilibrium was read the wrong way, so a source was called a sink or the reverse.

Sketch the phase line and read whether nearby solutions move toward the equilibrium or away from it, rather than reading a sign off the algebra.

8 wrong answers written to catch it · concept gap

The real part, the imaginary part, the modulus, and the argument of a complex number were interchanged when moving between rectangular and polar form.

Draw the number in the plane and read the modulus and the argument off the picture before you convert anything.

18 wrong answers written to catch it, 16 of them in complex analysis · concept gap

The named anatomical structure or gland does something other than the function described.

Name what the structure does before checking whether it matches the description. Working backwards from a familiar function invites the neighbouring structure.

256 wrong answers written to catch it, 238 of them in biological · concept gap

The chosen answer states an always, never, only, or all version of a finding that actually holds under stated conditions.

Treat always, never, only, and all as claims to be tested. Find the condition the real finding depends on, and see whether the option keeps it.

360 wrong answers written to catch it, 85 of them in biological · misread condition

The chosen term is the paired opposite of the right one, so the two members of a contrast pair were exchanged.

State both halves of the contrast pair and what distinguishes them before choosing one. Pairs are learned together and confused together.

179 wrong answers written to catch it, 64 of them in biological · concept gap

The transmitter chosen has a different primary role than the one the prompt describes.

Attach each transmitter to its main role and to the conditions it is implicated in, then match the prompt to that pairing.

57 wrong answers written to catch it, 44 of them in biological · concept gap

The described sleep phenomenon was attributed to a different stage of the sleep cycle.

Walk the cycle in order and attach each marker — spindles, delta waves, muscle atonia, rapid eye movement — to the stage it belongs to.

41 wrong answers written to catch it · concept gap

The hormone chosen is released by a different gland or produces a different effect than the one the prompt describes.

Name the gland that releases the hormone and the effect it produces, and check the prompt against both rather than against the name alone.

39 wrong answers written to catch it · concept gap

The division chosen — somatic, central, peripheral, or enteric — is not the autonomic branch the item describes, so the branching structure of the nervous system has not settled yet.

Walk down the branching structure — central and peripheral, then somatic and autonomic, then sympathetic and parasympathetic — before naming a division.

34 wrong answers written to catch it · concept gap

The chosen answer makes a single action potential grow or shrink with stimulus strength. Under the all-or-none principle each impulse is the same size, and intensity is carried by how often a neuron fires and how many neurons fire.

Hold on to the all-or-none principle: every impulse is the same size. Intensity is carried by how often a neuron fires and how many neurons fire.

14 wrong answers written to catch it · concept gap

The arousing and the calming branch of the autonomic nervous system were exchanged.

Decide first whether the described response arouses the body or calms it, and only then name the branch.

12 wrong answers written to catch it · concept gap

The answer names another memory store, long-term memory type, or working-memory component — episodic for semantic, procedural for declarative, iconic for echoic, the sketchpad for the loop — than the one the item describes.

Name the store and the type before answering: what it holds, how long it holds it, and what it is contrasted with.

57 wrong answers written to catch it, 37 of them in cognitive · concept gap

Encoding, storage, and retrieval were treated as interchangeable, so the failure or process was pinned on the wrong step.

Ask whether the information ever went in, whether it stayed in, or whether it could be found again, and pin the process on that step.

37 wrong answers written to catch it, 19 of them in cognitive · concept gap

The chosen answer gets the contingency backwards: it adds where the term removes, removes where the term adds, or weakens where the term strengthens.

Work out two things separately: whether something is added or taken away, and whether the behaviour goes up or down. The term is the combination of the two.

25 wrong answers written to catch it, 14 of them in cognitive · concept gap

The chosen answer describes classical conditioning where the item is about operant conditioning, or the reverse.

Ask whether the behaviour is drawn out by a signal that came first, or emitted and then followed by a consequence.

12 wrong answers written to catch it, 9 of them in cognitive · concept gap

The ability or conflict described belongs to a different stage or age band than the one chosen.

Place the ability or the conflict on the age timeline first, then read off the stage. Matching a stage name to a theorist is not the same as knowing when it happens.

85 wrong answers written to catch it, 67 of them in developmental · concept gap

The description was matched to a design with different sampling, timing, or control than the one specified.

Read who was sampled, when they were measured, and what was controlled. The design follows from those three facts, not from the topic.

169 wrong answers written to catch it, 57 of them in developmental · wrong method

The stages named are the right ones, but the sequence runs the wrong way.

Rebuild the sequence from the earliest stage upward before answering anything about order. Recognising the names is not the same as holding the order.

41 wrong answers written to catch it, 11 of them in social · concept gap

The described presentation was assigned to a neighbouring diagnostic class.

Check the described duration, symptom set, and level of impairment against the criteria before assigning a category. Neighbouring categories differ on exactly those.

122 wrong answers written to catch it, 111 of them in clinical · concept gap

The technique chosen belongs to another therapeutic tradition than the one named.

Ask what the technique assumes about how change happens, then name the school that holds that assumption.

90 wrong answers written to catch it · concept gap

The treatment or drug class named is real, but it is the first-line choice for a different disorder than the one described.

Name the condition first, then the treatment that is first-line for it. Working from a familiar drug back to a disorder picks up the wrong one.

19 wrong answers written to catch it, 18 of them in clinical · concept gap

The chosen answer treats variables that move together as proof that one produces the other, which the design cannot show.

Ask what the design could rule out. Without random assignment, variables that move together are an association and nothing more.

45 wrong answers written to catch it, 15 of them in clinical · wrong method

A real statistic was chosen, but one that answers a different question than the one asked (spread for centre, significance for magnitude, and so on).

Ask what the statistic is meant to answer — centre, spread, association, or whether a result is unlikely by chance — and choose on that basis.

108 wrong answers written to catch it, 86 of them in measurement · concept gap

Consistency of measurement was taken for accuracy of measurement, or the reverse.

Ask whether the question is about getting the same result twice or about measuring the thing you meant to measure. A test can do the first without the second.

132 wrong answers written to catch it, 76 of them in measurement · concept gap

The finding or theory named belongs to a different psychologist than the one the prompt describes.

Attach each name to the one finding it is known for, then check the description in the prompt against that finding rather than against the name's general area.

99 wrong answers written to catch it, 38 of them in measurement · concept gap

The historical school chosen holds a different position than the one the prompt describes.

Ask what the school took psychology's subject matter and its method to be, then match the description to that position.

206 wrong answers written to catch it, 77 of them in history · concept gap