Most marks aren’t lost to hard maths — they’re lost to a dozen recurring, nameable errors. Our question bank builds its wrong options from these exact mistakes, so we can tell you precisely which ones you make. Here’s the catalogue: what each one is, why your brain does it, and the fix.
Percentage change is always measured against the ORIGINAL value: (new − old) ÷ old.
The fixThe most common table mistake isn't arithmetic at all — it's pulling the number from the row above, the column beside, or a similarly named header, then computing perfectly with the wrong data.
The fix"What share is X?" means X ÷ (the relevant total).
The fixAn answer that's exactly 10× or 100× off isn't a maths error — it's a decimal slip: a percentage not converted (×5 instead of ×0.
The fixCombining two group means by simple averaging is only valid when the groups are the same size.
The fixSpeed = distance ÷ time, and the other two follow by rearrangement: distance = speed × time, time = distance ÷ speed.
The fixConverting with a rate goes one way; the return trip divides.
The fixA multi-step question's intermediate result is almost always among the answer options.
The fixIn True/False/Cannot-say questions, 'Cannot say' is correct whenever the statement needs information the exhibit doesn't contain — however plausible the statement sounds.
The fixComputing the probability (or percentage) of the event when the question asked for its opposite — or vice versa.
The fix"Which grew most?" has two correct answers depending on the question: the biggest absolute change (in units) or the biggest relative change (in %).
The fixTwo years of 10% growth is ×1.
The fix