KS2 SATs 2025 — Mathematics Paper 1: Arithmetic

The idea

Fluent mathematicians do not just calculate — they check. Every operation has an inverse that undoes it: addition is undone by subtraction, and multiplication is undone by division. After a calculation, run the inverse to see whether you land back on the starting number.

Estimation is the other safety net. Round each number to a friendly value and do a quick mental calculation. Your real answer should be close to the estimate. If it is wildly different, a place-value or carrying slip has probably crept in.

Use these checks across the whole arithmetic paper: column methods, fractions, decimals and percentages alike. A twenty-second check on a long question is worth far more than rushing on and carrying a wrong answer with you.

Worked example

Work out 1,248 ÷ 16, then check your answer.

1. 16 × 70 = 1,120. Subtract: 1,248 − 1,120 = 128.
2. 16 × 8 = 128 exactly, so the answer is 70 + 8 = 78.
3. Check with the inverse: 78 × 16 = 1,248, which matches the starting number.

Answer: 78

Watch out

• Checking by repeating the same method, which repeats the same slip.
• Estimating so roughly that a genuinely wrong answer still looks close.