Centimetres

In your book, Maths Mela (Chapter 6), Chutki wants to keep track of how tall her plant grows each week. A metre rope is too long to measure a small plant, or an eraser, or a grain of rice. We need a smaller unit.

Look at a metre scale or a tailor's measuring tape. It is divided into 100 equal parts. The length of each small part is called a centimetre, written cm. The gap between two marks next to each other is 1 cm. When 1 cm is repeated 100 times, we get 1 metre. So 1 m = 100 cm.

Now we can say the rope lengths in centimetres. Half a metre is half of 100 cm: 1/2 m = 50 cm, because 50 + 50 = 100. A quarter metre is one of four equal parts of 100 cm: 1/4 m = 25 cm, because 25 + 25 + 25 + 25 = 100. Three quarters of a metre is 25 + 25 + 25 = 75 cm, so 3/4 m = 75 cm.

The book puts these on a number line. Above is 0 m to 1 m; below is 0 cm to 100 cm. 1/4 m sits at 25 cm, 1/2 m at 50 cm, 3/4 m at 75 cm, and 1 m at 100 cm.