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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.
