Year 3 Maths Number & Algebra

Introduction to Decimals

A decimal is a number with a point that separates the whole number part from the parts less than one. Decimals help us show values between whole numbers.

The Decimal Point

The dot in a decimal number is the decimal point. Digits to the left are whole numbers. Digits to the right are parts of a whole.

3 . 7

whole part

Tenths

If you split 1 whole into 10 equal parts, each part is one tenth = 0.1. So:

0.1 = one tenth
0.5 = five tenths = half
0.9 = nine tenths
1.0 = ten tenths = one whole

Decimals on a Number Line

Between 0 and 1, there are 10 equal jumps of 0.1 each.

0.1 0.2 0.3 0.5 0.7 0.9

Real-Life Decimals

🌶 Length: 1.5 metres (1 metre and a half)
💲 Money: $2.50 (2 dollars and 50 cents)
⚖ Temperature: 36.6°C (body temperature)
✍ Score: 8.5 out of 10

Place Value with Decimals

Let's look at the number 4.7:

ONES

4 ones

TENTHS

7 tenths

4.7 = 4 whole + 7 tenths = four and seven tenths

Key Vocabulary

decimal — a number with a decimal point separating the whole and part

decimal point — the dot that separates whole numbers from parts less than one

tenths — parts you get when 1 whole is split into 10 equal pieces

place value — the value of a digit based on its position in a number

Lesson Summary

✓A decimal uses a decimal point to separate whole numbers from parts less than one.
✓Tenths are what you get when 1 whole is split into 10 equal parts. One tenth = 0.1.
✓In 3.7, the 3 is in the ones place and the 7 is in the tenths place.
✓0.5 = one half. Decimals appear in measurements, money, and everyday life.