ISEE Quantitative Reasoning common mistakes
ISEE Quantitative Reasoning · Understand the traps and how to avoid them.
On Quantitative Comparison items, the candidate computes both quantities fully and marks the answer based on which numeric result 'looks bigger', instead of comparing them structurally (e.g., cancelling a shared term or substituting one test value).
The four comparison answer choices (A: Quantity A greater, B: Quantity B greater, C: equal, D: cannot be determined) invite arithmetic, so candidates default to number-crunching under time pressure and never test the 'cannot be determined' case with a second value.
What to do instead
Adopt a fixed routine: simplify both quantities symbolically first, then plug in two contrasting values (one positive, one negative or a fraction) before choosing. If the two values give different orderings, the answer must be D. Practice 15 comparison items a session until the routine is automatic.
The candidate solves a word problem correctly but answers the wrong quantity - giving the number of boys when the question asked for girls, or the discounted price when it asked for the discount amount.
Working memory is consumed by the multi-step arithmetic, so the final question sentence is skimmed rather than re-read after the computation.
What to do instead
Before computing, underline the exact quantity requested and write a one-line label next to the answer blank (e.g., 'answer = discount $'). After computing, re-read the final sentence and confirm units and label match. Build this as a two-second habit on every word problem.
The candidate treats 'cannot be determined' as a last-resort guess on Quantitative Comparison and almost never selects it, even when the relationship genuinely depends on an unspecified value.
Test-takers are trained that a definite answer is 'safer', and D feels like admitting defeat; also, many candidates only test one value, which always produces a definite ordering.
What to do instead
Train a deliberate D-hunt: for every comparison item with a variable, force yourself to find one value that flips the ordering before ruling D out. Track a log of items where D was correct and review why, so the choice stops feeling like a guess.
On reading comprehension, the candidate selects an answer that is true according to general knowledge or personal opinion but is not stated or implied in the passage.
Familiar topics trigger prior knowledge, and plausible-sounding choices feel correct because they are factually true in the world, not because the passage supports them.
What to do instead
For every answer choice, point to the specific sentence or lines in the passage that justify it; if you cannot locate support, eliminate it. Treat the passage as the only source of truth and practice 'line-citing' every correct answer during review.
The candidate picks an answer choice that overstates the passage - using absolute words like 'all', 'never', 'proves', or 'always' when the passage used hedged language like 'some', 'may', or 'suggests'.
Strong, confident-sounding options feel more like correct answers, and candidates do not compare the strength of the claim in the choice against the strength of the claim in the text.
What to do instead
Circle every absolute qualifier in the answer choices and check it against the passage's own wording. Prefer choices whose hedging matches the passage. Drill with paired choices that differ only in qualifier strength so the distinction becomes visible.
On sentence-equivalence or vocabulary-in-context items, the candidate chooses a word because it is a synonym of the target word in isolation, ignoring whether the sentence's logic (contrast, cause, definition) supports it.
Vocabulary is retrieved as a dictionary meaning rather than as a contextual fit, and candidates skip identifying the sentence's structural clue word (e.g., 'although', 'because', ';').
What to do instead
Before looking at choices, locate the signal word or punctuation and predict the blank's meaning in your own words. Then pick the choice closest to your prediction, not the most impressive-sounding word. Practice predicting before reading options on every item.
The candidate runs out of time and leaves questions blank at the end of a section because they spent too long on a single hard item early on.
Sunk-cost persistence on one problem, plus no pre-set time budget per question, means the candidate only discovers the time problem when the section is nearly over.
What to do instead
Set a per-question ceiling (roughly one minute on Quantitative Reasoning, slightly more on reading) and a hard rule: after the ceiling, mark the best guess, flag it, and move on. Do timed full-section practice so pacing becomes calibrated rather than hopeful.
The candidate misreads the question stem's operation - solving for x when asked for 2x, or answering 'which is NOT true' as if it asked 'which is true'.
Speed-reading the stem and pattern-matching to a familiar problem type causes the candidate to skip small but decisive words like 'not', 'except', 'least', or 'in terms of'.
What to do instead
Circle negation and target words in the stem before solving. On 'NOT/EXCEPT' questions, mark each choice T or F as you evaluate it, then select the odd one out. Review errors by classifying whether the miss was conceptual or a stem misread.
On geometry items, the candidate assumes a figure is drawn to scale and estimates lengths or angles visually instead of using given measurements and properties.
Diagrams are persuasive, and estimation feels faster than setting up the relationship; candidates also forget that figures may be explicitly not drawn to scale.
What to do instead
Redraw or annotate the figure with the given values and mark unknown angles or sides with variables. Use only stated measurements and known properties (triangle angle sum, parallel-line angles, area formulas). Never infer a length or angle from appearance alone.
The candidate answers a multi-step percentage or ratio problem by applying operations in the wrong order - e.g., adding a 20% markup and a 20% discount and concluding the price is unchanged.
Percent changes are treated as additive quantities rather than multiplicative factors, and the candidate does not translate the sequence into a single expression.
What to do instead
Convert every percent change to a multiplier (increase 20% → ×1.2; decrease 20% → ×0.8) and chain them in one expression before computing. Sanity-check by asking whether the result should be above or below the original, and practice mixed percent/ratio chains until the multiplier method is reflexive.