Common Exam Mistakes

Most marks lost in OCR GCSE Mathematics (J560) are not lost because a student couldn't do the maths — they are lost to avoidable, repeated slips: rounding too early, dropping units, misreading a scale, or simply not answering the question asked. The encouraging side of that is these are the easiest marks to win back, because fixing them needs habits, not new knowledge. This lesson is a teacher's-eye tour of the cross-topic mistakes that recur on every paper and tier, with the practical fix for each. Think of it as a pre-flight checklist for your working.

Avoiding these errors protects marks across all three objectives: accuracy slips cost AO1 marks, failing to communicate or justify costs AO2, and answering the wrong question or mis-checking costs AO3. Strong exam technique is, in large part, simply not throwing marks away. For many students, eliminating these recurring slips lifts their grade more than any amount of new content learning — because the marks were within reach all along.

A Quick-Reference Table of Slips and Fixes

Common mistake	Why it loses marks	The fix
Rounding too early	Final answer drifts outside the accepted range	Keep full accuracy; round only at the end to the stated degree
Dropping units	Units are often a separate B mark	Always state units; check they match the quantity (cm vs cm²)
Misreading scales	Wrong value read from axis/ruler/protractor	Work out the value of one small square/division first
Not answering the question asked	You solve a different problem	Re-read the question after finishing; underline what is asked
No working shown	A wrong answer with no working scores zero	Show method so M marks survive a slip
Wrong form of answer	Decimal given when fraction/surd was required	Re-check the demanded form before moving on
Calculator mis-keying	Order of operations applied wrongly	Use brackets; estimate to check the magnitude

The rest of this lesson takes the most damaging of these in turn. The common thread is that none of them is about not knowing the maths — every one is a presentation, accuracy or reading error layered on top of correct understanding. That is good news, because habits are far quicker to fix than knowledge gaps.

Rounding Too Early

This is the most expensive habit on the calculator papers. If you round a partway value and then keep calculating, the rounding error grows and can push your final answer just outside the band the mark scheme accepts.

Worked Example

A right-angled triangle has legs of $5$5 cm and $7$7 cm. Work out the length of the hypotenuse, giving your answer to 1 decimal place.

Correct — full accuracy held: $h = \sqrt{5^{2} + 7^{2}} = \sqrt{25 + 49} = \sqrt{74} = 8.6023\ldots$h=52+72​=25+49​=74​=8.6023…, which rounds to $8.6$8.6 cm. Answer: $8.6$8.6 cm.

Faulty — rounding $\sqrt{74}$74​ to a whole number mid-way would give $9$9, and any further step built on $9$9 would now be wrong. The rule: carry every digit (or keep the value in Ans/memory) and round once, at the end.

The same trap appears in trigonometry and in any multi-stage calculation. If a question asks you to find an angle and then use that angle in a further calculation, rounding the angle to, say, the nearest degree before reusing it can shift the final answer enough to fall outside the accepted range. Carry the full unrounded value (store it in memory), use it in the next step at full precision, and only round the final quantity to the accuracy the question states. A useful mental flag: the words "give your answer to…" tell you when to round — at the very end, once, to that degree — and nowhere before.

Missing or Wrong Units

A "Work out" answer is often not complete without its units, and the units are frequently their own mark. The trap that catches the most students is confusing length units with area or volume units.

Quantity	Correct unit form
Length / perimeter	cm, m, km (linear)
Area	cm², m² (square)
Volume / capacity	cm³, m³, litres (cubic)
Speed	km/h, m/s (compound)

If you calculate an area and write "$48$48 cm" instead of "$48\text{ cm}^{2}$48 cm2", you can lose the units mark even though the number is right. After every answer, ask: does this quantity have units, and are they the right kind?

Misreading Scales

Graphs, number lines, rulers and protractors all use scales — and not every small square is worth 1. Reading the scale wrongly turns a correct method into a wrong answer.

Worked Example

On a graph, the $y$y-axis runs from $0$0 to $50$50 and there are $10$10 equal gridlines between them. A point sits on the fourth gridline up. What is its $y$y-value?

First find the value of one division: $50 \div 10 = 5$50÷10=5 per gridline. The fourth gridline is $4 \times 5 = 20$4×5=20. Answer: $y = 20$y=20. A student who assumes "one square = 1" would read $4$4 — wrong by a factor of 5. Always work out the value of one small division before reading any point. The same applies to a protractor: check whether you are reading the inner or outer scale, and from which zero.

Not Answering the Question Asked

Examiners see this constantly: a perfectly correct calculation that answers a subtly different question. The classic pairs are revenue vs profit, perimeter vs area, the value of $x$x vs the value of an expression in $x$x, and "how many more" vs "how many".

Worked Example

Solve $2x + 3 = 11$2x+3=11, and hence write down the value of $x + 1$x+1. A student stops at $x = 4$x=4 and writes that as the answer. But the question asks for $x + 1$x+1, which is $4 + 1 = 5$4+1=5. Answer: $5$5. The fix is mechanical: when you finish, re-read the question and check your answer matches what was asked — including any "hence", "in total", "to the nearest…", or "give your answer as a percentage".

Showing Too Little — or Nothing

A surprising number of marks are lost not to a wrong method but to no visible method. A student does the working in their head or on the calculator, writes down a single final number, and gets it slightly wrong — scoring zero on a question they almost solved. Had the method been on the page, the M marks (and any follow-through) would have survived the slip.

Worked Example: the cost of no working

Consider a 3-mark question: Work out the mean of $4, 7, 9, 12$4,7,9,12. A student types it into the calculator, mis-keys, and writes "$7$7". With no working, that earns nothing. The same student showing the method — $\dfrac{4 + 7 + 9 + 12}{4} = \dfrac{32}{4} = 8$44+7+9+12​=432​=8 — would earn the method mark even if the final arithmetic slipped. The correct answer is $8$8, but the point is that visible working is a safety net. Treat every question worth more than one mark as one where the working must be on the page.

Reading the Question in Full