Today we will be learning: to solve mathematical puzzles that subtraction is the inverse of addition...

Today we will be learning:

• to solve mathematical puzzles

• that subtraction is the inverse of addition

• that division is the inverse of multiplication.

Mental Activity

We are going to practise solving some number problems.

I bought two packets of crisps which cost 25p each. How much did they cost altogether?

50p

How much change did I have from 70p?

20p

I had 12 conkers, James gave me 11

more and I lost 9. How many did I have left?

14

I bought some sweets for 15p and a pencil for 16p. How much change from

50p did I get?

19p

I had 4 packets of 5 sweets. I ate 6 sweets.

How many did Ihave left?

14

I had 20 marbles. I lost half of them and gave 5 to my friend. How many

did I have left?

5

I bought two bars of chocolate costing 31p

each and an apple costing 17p. How much

did I spend?

79p

Main Activity

Today we are going to solve mathematical problems.

?I am thinking of a number.

I halve it. My answer is 6.

What is my number?

Main Activity

Today we are going to solve mathematical problems.

12I am thinking of a number.

I halve it. My answer is 6.

What is my number?

?

I am thinking of another number.

I add 2.

What is my number?

I double the answer.

I get a total of 10.

?

How can we do this? I add 2.

What is my number?

I double the answer.

I get a total of 10.We need to work

backwards.

Half of 10 = 5

10 2 = 5

5 – 2 = 3

So the mystery number is

3

How can we do this? I add 2.

What is my number?

I double the answer.

I get a total of 10.We need to work

backwards.

Half of 10 = 5

10 2 = 5

5 – 2 = 3

So the mystery number is

Top Tip

Halving (division) and doubling (multiplication) are inverse operations.

Inverse means

opposite.

What does “inverse” mean?

+ - x

Here are the signs for the four number operations.

Which number operations are related?

What is the inverse of addition?

Subtraction.

Group Work

Solve one-step number problems.

Work in pairs. Make up one-step number puzzles for your partner to solve.

Work in pairs. Make up two-step number puzzles for your partner to solve.