Adding and subtracting masses

Worked example 1

38 kg 600 g + 27 kg 700 g

Step 1 Add the grams: 600 + 700 = 1 300 g.

Step 2 1 300 g = 1 kg 300 g. Keep 300 g and carry 1 kg.

Step 3 Add the kilograms: 38 + 27 + 1 = 66 kg.

Together they brought 66 kg 300 g.

Worked example 2

38 kg 600 g − 27 kg 700 g

Step 1 600 g take away 700 g? Not enough! Break 1 kg into 1 000 g. Now there are 1 000 + 600 = 1 600 g, and 37 kg.

Step 2 Subtract the grams: 1 600 − 700 = 900 g.

Step 3 Subtract the kilograms: 37 − 27 = 10 kg.

On Monday they brought 10 kg 900 g more. Check: 10 kg 900 g + 27 kg 700 g = 38 kg 600 g.

Worked example 3

2.5 kg + 1.75 kg. Write 2.5 as 2.50. Then 2.50 + 1.75 = 4.25 kg.

Worked example 4

A sack holds 50 kg of rice. The shop sells 12.75 kg. How much is left? Write 50 as 50.00. Then 50.00 − 12.75 = 37.25 kg.

Worked example 5

A lorry can carry 5 t. It already has 3 t 400 kg of cement. How much more can it carry?

Step 1 Change to kg: 5 t = 5 000 kg and 3 t 400 kg = 3 400 kg.

Step 2 5 000 − 3 400 = 1 600 kg.

Step 3 1 600 kg = 1 t 600 kg.