Money and Conversions Worked ExamplesIGCSE Maths 0580

Decide multiply or divide by sense-checking the size. One US dollar is worth more than one Singapore dollar, so a US amount must give a bigger number of Singapore dollars. If your answer went the wrong way, you used the wrong operation. The June 2025 examiner report found that the most common error on a conversion like (b) was multiplying by the exchange rate instead of dividing by it.

The single-multiplier method ($\times 0.98$) is faster than calculating $2\%$ and subtracting — but get the decimal right: on a percentage-fee question, the March 2026 examiner report noted that "Some candidates used the incorrect multiplier 0.5 instead of 0.05 to find 5%." Here $2\% = 0.02$, not $0.2$. Also check the direction: a commission is taken off what the customer receives, whereas a booking fee is added to what they pay. Money answers need two decimal places — write $661.50$, not $661.5$.

Two things are needed: converting kilograms to grams before comparing, and a clear statement of which is best. Note the biggest pack is the worst value here, so do not assume that bigger is cheaper.

Do not round the intermediate value, and do not round the final answer when it is an exact amount of money. The March 2026 examiner report noted that some candidates rounded an exact currency answer to $3$ significant figures, even though an exact amount of money was required. The same report found a few candidates multiplying by an exchange rate instead of dividing, so check each step against the size of the currencies.

Percentage profit divides by the cost price, not the selling price. Dividing by $5400$ gives $6.7\%$ — a plausible-looking wrong answer and a common error.

Do not add $20\%$ to $68 — that gives $81.60 and is wrong, because the $20\%$ was taken off the larger original price, not the sale price. Reverse percentages always divide by the multiplier.

In (b), reading off a small value such as €50 and multiplying by $24$ magnifies any reading error — choose the point where the line crosses a grid intersection exactly. Always check which axis you start from: converting dollars to euros means starting on the vertical axis.

Multiplying by the rate instead of dividing (for example $189 \times 0.79 = 149.31$) is a common error (the June 2025 examiner report found multiplying instead of dividing was the most common error on a currency conversion) — sense-check that £189 should be more than $189$ dollars because each pound is worth more than a dollar. In (c), a bare 'yes' scores nothing: both values and the comparison must be shown.

The fixed fee means line $A$ does not pass through the origin, so its rate is its gradient, not a single reading divided by another: $540 \div 480 = 1.125$ is wrong. In (e), a graph answer is not possible because £800 is off the scale — form the two expressions and calculate.

Show the conversions — they earn a method mark even if the order slips. The March 2025 examiner report found errors converting millimetres to centimetres or metres, and that "Many found the conversion of 0.00002km the hardest." For kilometres, go in steps: $0.00061\text{ km} = 0.61\text{ m} = 610\text{ mm}$.

On a similar question, the June 2025 examiner report found that "Common errors included finding the difference in cost of gallons rather than litres, or in pounds rather than dollars." Answer in the units the question asks for — here dollars per litre — and name the cheaper country as well as the difference.

The June 2025 examiner report noted that a common error on the area conversion was dividing by $100$ instead of $10\,000$, and that using the wrong factor on the volume conversion led to two common incorrect answers. Square the length factor for area and cube it for volume.