Calculator skills and types of number

A calculator is only as good as the person using it. Learn to key in calculations correctly, make sense of the answer, and meet the different types of number.

Practise this lesson free (7 questions)

Keying it in

Use brackets for anything on top of or under a fraction line.
(4.2 + 7.8)(2.5 × 1.6) is typed as (4.2 + 7.8) ÷ (2.5 × 1.6) = 12 ÷ 4 = 3.
Squaring a negative needs brackets: (−3)2 = 9, but −32 means −(32) = −9.
Estimate first so you notice a keying mistake.

Making sense of the answer

Round to fit the context.
230 people in 52-seat coaches: 230 ÷ 52 = 4.42..., so you need 5 coaches.
Money: a display of 4.5 means £4.50.
Time: 2.75 hours is 2 hours 45 minutes.

Types of number

Integers: whole numbers, positive, negative or zero.
Rational numbers: can be written as a fraction of two integers, such as 34, −5 or 0.333... = 13. Terminating and recurring decimals are rational.
Irrational numbers: cannot be written as a fraction of two integers. Their decimals never end and never repeat, such as √2 and π.
These sets are infinite: there is no largest integer, and between any two different fractions there is always another one.
Worked example

Work out (5.6 + 2.8)(0.4 × 3).

  1. Top: 5.6 + 2.8 = 8.4
  2. Bottom: 0.4 × 3 = 1.2
  3. Type (5.6 + 2.8) ÷ (0.4 × 3)

Answer: 7

Key idea

Put brackets round the top and bottom of a fraction. Round answers to fit the context. Rational numbers can be written as fractions; irrational numbers like √2 and π cannot.

Key words
Estimate
An approximate answer, often found by rounding each number to 1 significant figure first.
Time
60 seconds = 1 minute, 60 minutes = 1 hour. 0.5 hours = 30 minutes, 0.25 hours = 15 minutes.
Integer
A whole number. It can be positive, negative or zero.

All KS3 Mathematics key terms and definitions →

Common mistakes
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Extra practice

2 more questions

Try each one, then tap to check.

  1. Use a calculator to work out (5.6 + 9.4)(1.25 × 2.4).

    Show the answer

    Answer: 5

    Top: 15. Bottom: 3. 15 ÷ 3 = 5.

  2. Use a calculator to work out √(6.52 − 2.52).

    Show the answer

    Answer: 6

    42.25 − 6.25 = 36, and √36 = 6.

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Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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