Primary Maths Percentages: Identify the Whole Before You Calculate

Ask what the percentage is a part of

A question in the KiasuParents MathsGuru discussion asks what percentage of a person’s July salary was spent. The important reading skill is identifying the whole being used for the comparison. Two correct money amounts can still lead to an incorrect percentage if they are divided in the wrong order. The worked situations below are original examples, not a reproduction of the forum problem.

Before calculating, ask your child to complete this sentence: the amount spent is being compared with ___. Underline the words that identify that whole. If the question says percentage of July salary, the whole is July salary. It is not automatically the amount left over, the previous month’s salary or the total of two salaries.

Keep the amount and the percentage separate

In an invented example, July salary is $2,400 and spending is $600. The fraction spent is 600/2400 = 1/4, so the percentage spent is 25%. The amount spent remains $600. Put units beside the money amounts so that an answer of $25 or 600% looks immediately suspicious.

Draw a bar representing the $2,400 whole and split it into four equal sections. Shade one section for spending and leave three for the remainder. This gives a visual check: $1,800 is left, which is 75% of that same whole. Spent and remaining percentages add to 100% here because they account for the complete salary.

Notice when the whole changes

Suppose the next question asks what percentage of the remaining $1,800 the $600 spending represents. Now the calculation is 600/1800 × 100%, or 33 1/3%. The money amounts have not changed, but the reference amount has. Explain the difference in words before deciding whether a previous answer can be reused.

For another comparison, a price rises from $80 to $100. The increase is $20 and the percentage increase is 20/80 × 100% = 25%. A fall from $100 back to $80 is a 20% decrease. The changes use different starting amounts, so equal dollar changes need not have equal percentage sizes.

Work backwards from a percentage

If 25% of a salary is $600, then 1% is $24 and the complete 100% is $2,400. A child may instead recognise that 25% is one quarter and multiply by four. Ask why their method recovers the whole. Do not accept a sequence of calculator steps without knowing what each number represents.

Try a short pair of questions using the same figures, first finding a percentage and then finding the whole. Ask your child to label which quantity is unknown. This helps separate two problem types that can otherwise look almost identical on a worksheet.

Use a three-line correction

Write the part, the whole and the comparison as three lines. If an answer is wrong, identify whether the mistake came from reading the whole, finding the relevant amount or doing the arithmetic. Choose a different question with the same comparison structure and retry it without the worked answer visible.

Choose a suitable practice question from our Primary Maths papers, checking the level, year and original instructions.

Sources and further reading

Checked on 7 November 2026. The linked discussion is real; worked examples and practice routines are our original guidance. Older discussions are not evidence of current examination rules.

• Tutor MathsGuru: Ask me for your burning Maths questions! — Exact post date unavailable in the accessible discussion excerpt.