An 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 ×0.05), a unit boundary missed (£000s), or a calculator entry with the point in the wrong place.
Percentages, 'in thousands' footnotes and unit conversions all silently move the decimal point. The working feels identical either way, so nothing alerts you — and the test helpfully offers the 10×-off answer as an option.
Estimate first, always: "5% of 3,400 is about 170" takes two seconds and makes 1,700 impossible to accept. Read exhibit footnotes for units before computing, and treat any suspiciously round 10×-relationship between your answer and an option as an alarm, not a coincidence.
A council's budget is £24m and the population is 137,000. What is the spend per person?
Per-person rate = total amount ÷ population. Watch the magnitude (thousands vs millions). The correct answer is £175.18. Traps to avoid: £1,751.82 comes from the "decimal slip" error; £5.71 comes from the "inverted rate" error; £128.34 comes from the "wrong pop" error; £17.52 comes from the "wrong base" error.
This trap appears in 47 of our questions, across: Nested proportion · Per-capita rate · Percentage of · Mental percentages · Fraction–decimal–percent.
The free diagnostic doesn’t just score you — it names the mistakes behind your wrong answers, this one included.
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