Use Mental Methods of Addition and Subtraction to Solve Word Problems

When you add, things get bigger, longer or more.

Example

Jane has 12 pencils and Bill has 15 pencils.

How many do they have in total?

Answer

Add together 12 + 15.

The easiest way to do this is to split the second number into tens and ones. If we split 15, we get 1 ten and 5 ones.

Start at 12 and add 10:   12 + 10 = 22

Then add on the 5 ones: 22 + 5 = 27

They have 27 pencils in total.

When you subtract, things get smaller, shorter, fewer or less.

Example

Jane has 27 marbles and gives 15 to her brother Bill.

How many does she have left?

Answer

Subtract: 27 - 15.

Once again, split the second number into tens and ones. 15 is 1 ten and 5 ones.

Start at 27 and take away 10: 27 - 10 = 17

Then take away the 5 ones: 17 - 5 = 12

Jane has 12 left.

Are you ready to have a go at some questions?