Units of Measurement

Class 7 Maths · Chapter 3: A Peek Beyond the Point · NCERT Ganita Prakash section 3.5

Learn

Length: 1 cm = 10 mm, so 1 mm = 0.1 cm. Then 5 mm = 0.5 cm, 12 mm = 1.2 cm, and 5.6 cm = 56 mm. Also 1 m = 100 cm, so 1 cm = 0.01 m: 15 cm = 0.15 m and 2.07 m = 207 cm. A human hair is only about 0.1 mm thick!

1 mm = 0.1 cm · 1 cm = 0.01 m

Weight: 1 kg = 1000 g, so 1 g = 0.001 kg. Then 5 g = 0.005 kg, 10 g = 0.010 kg = 0.01 kg, and 254 g = 2/10 + 5/100 + 4/1000 kg = 0.254 kg. Also 1 g = 1000 mg, so 1 mg = 0.001 g.

254 g = 0.254 kg

Money: 100 paise = ₹1, so 1 paisa = ₹0.01. 75 paise = ₹0.75, 5 paise = ₹0.05 and 250 paise = ₹2.50. Paise coins of 25 and below were withdrawn in 2011, but paise still appear on bills and bank statements.

75 paise = ₹0.75

A pattern: 1 m = 100 cm = 1000 mm, so 1 mm = 0.001 m. Each time we divide a unit by 10, the digits move one place to the right of the point. Ask your grandparents what things cost when they were young: maybe a dosa for 50 paise (₹0.50)!

Explore: match the measures.

1. Match each measure to the same amount in the bigger unit.

Remember

• 1 mm = 0.1 cm; 1 cm = 0.01 m; 1 g = 0.001 kg; 1 paisa = ₹0.01.
• Changing to a unit 10, 100 or 1000 times bigger moves the digits 1, 2 or 3 places to the right of the point.

Quick check

How many kilograms is 68 g?

1. 0.068 kg
2. 0.68 kg
3. 6.8 kg
4. 0.0068 kg

Think about it

How many millimetres make 1 kilometre?

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.