Solving problems involving mass

When you add, subtract, multiply or divide mass in grams and kilograms, sometimes you need to convert the measurements so that they are in the same unit.

You can use this fact:

1 kilogram = 1,000 grams

You can also write it like this:

1kg = 1,000g

To convert from kilograms to grams you multiply by 1,000.

To convert from grams to kilograms you divide by 1,000.

Test out your knowledge of how to solve problems involving mass with this quiz, then read on to complete the page.

The mass of these oranges is 500g and the mass of these apples is 600g.

Together the mass of the oranges and apples is 1,100g.

To convert this mass into kilograms and grams, remember:

1 kilogram = 1,000 grams

As 1,100g is greater than 1,000g, you can split it into 1,000g (which is 1 kilogram) and the remaining 100g.

So:

1,100g = 1kg 100g

You can also write this as a decimal in kilograms.

To do this, divide the total number of grams by 1,000.

For example:

1,100 ÷ 1,000 = 1.1

So, 1,100g can also be written as 1.1kg.

How to subtract kilograms and grams

The mass of the pineapple is 1.2kg or 1kg and 200 grams.

The mass of the strawberries is 700 grams.

To find the difference between the mass of the pineapple and strawberries, first convert the mass of the pineapple into grams.

1 kg 200g = 1,200 grams

Then, subtract the mass of the strawberries.

1200g - 700g = 500g

The pineapple is 500 grams heavier than the strawberries.

You can represent this on a number line.

You could also use the counting on method to find the difference here, counting on in hundreds from 700 to 1,200.

How to divide kilograms

You can divide measurements of mass in the same way that you divide other values.

Before you start to calculate, check if any values in the problem need converting from kilograms to grams, or grams to kilograms.

Think about the problem:

1.8kg ÷ 6 = ?

To divide 1.8kg by 6, first convert 1.8kg into grams by multiplying it by 1,000.

1.8 × 1,000 = 1,800

So 1.8kg = 1,800 grams.

Then divide 1,800 by 6.

1,800 ÷ 6 = 300

Therefore:

1.8kg ÷ 6 = 300g

This division is shown in the bar model below.