Decimals: the little point
๐ In short
On a shop's scales we might read 1.5 kg, and in a race 9.58 seconds. These are decimal numbers: a point separates the whole part from small parts smaller than one. 1.5 means one and a half.
๐คฉ Did you know?
- The world record for the 100 meters is 9.58 seconds, set by Usain Bolt in 2009.
- A healthy person's body temperature is about 37 degrees; if it reaches 38.5, they have a fever.
- 0.5 is a half, and 0.25 is a quarter.
- The Muslim scholar Ghiyath al-Din al-Kashi explained decimal fractions in his book โThe Key to Arithmeticโ in 1427.
๐ Find out more
๐ Tenths
If we split one into 10 equal parts, each part is a โtenthโ, written 0.1. The first digit after the point is the tenths: 2.3 means 2 and 3 tenths.
๐ Hundredths
If we split one into 100 parts, each part is a โhundredthโ, written 0.01. The second digit after the point is the hundredths: 4.25 means 4 and 25 hundredths.
๐ก Comma or point
In some countries the decimal mark is a point, 2.5, and in others a comma, 2,5. The meaning is the same. What matters is reading it: two point five, that is two and a half.
๐ฏ In our lives
We find decimals in prices, heights (1.35 m), weights, temperatures (37.5ยฐ) and race results, where a runner can win by a hundredth of a second!
๐งฎ Worked examples
- 0.5 = 5/10 = 1/2Five tenths is a half.
- 1.5 m = 150 cmA meter and a half.
- 2.4 + 1.3 = 3.7Add tenths to tenths and ones to ones.
๐ Key words
- Decimal number
- A number with a decimal point, like 3.5
- Tenth
- One of ten equal parts of one: 0.1
- Whole part
- What comes before the point in a decimal
๐งช Try it at home
Measure your height with a tape measure and write it in centimeters, then in meters as a decimal (like 132 cm = 1.32 m). Do it for everyone in your family and put them in order from shortest to tallest.
๐งฉ Test yourself
1 What does 3.5 mean?
2 Which is bigger: 0.7 or 0.25?
3 How many centimeters are in 1.5 meters?