Which proportion is shaded (tenths)?

Decimal Numbers

You already know whole numbers: 1, 2, 3, 10, 25 … But what if we need a number between two whole numbers — like half a litre of juice, or 1 dollar and 50 cents? We use decimal numbers!

A decimal number has two parts separated by a decimal point (.):

3.4 = 3 whole units + 4 tenths

Tenths

Cut a chocolate bar into 10 equal pieces. Each piece is one tenth, written as 0.1. The strip below has 10 boxes — each orange box equals $1/10$. We can also write it as 0.1.

When all 10 boxes are filled, we get 1 whole:   $0.1 × 10 = 1$

If we eat 3 pieces, we have eaten $3/10$, or 0.3 (three tenths).

And if we eat half of it, we have eaten $5/10$, or 0.5 (five tenths).