*This quiz addresses the requirements of the National Curriculum KS1 Maths and Numeracy for children aged 6 and 7 in year 2. Specifically this quiz is aimed at the section dealing with checking calculations using the inverse operation. *

In order to check a calculation, it is useful to know the inverse (or opposite) operation. For example, the inverse operation of addition is subtraction so to check 5 + 6 = 11, you could try 11 - 6 = 5 or 11 - 5 = 6. Another way of checking an addition calculation would be to add the numbers up in a different order - this of course does not work for subtraction!

Question 1

How could you check 62 + 38 = 100?

By taking away 100

By finding the difference between 62 and 38

By subtracting 100 from 62

By subtracting 38 from 100

If 62 + 38 = 100 is correct, then 100 - 38 should give an answer of 62

Question 2

How would you check 45 - 23 = 22?

By subtracting 22 from 23

By adding 45 and 22

By finding the total of all the numbers

By adding 23 and 22

Adding the two smaller numbers should give the larger number

Question 3

Use number pairs, or bonds, to 20 to find the incorrect calculation:

20 - 10 = 20

20 - 0 = 20

20 - 15 = 5

20 - 19 = 1

20 + 10 would not give a total of 20

Question 4

If 29 - 15 = 14, what could you do to check the answer?

Subtract the numbers in a different order

Add 15 and 14 together

Take out any harder numbers

Put 14 at the beginning of the calculation

You can use addition to check a subtraction

Question 5

Which calculation could you use to check that 16 - 9 = 7 is correct?

16 + 9 = 7

9 + 7 = 16

7 - 16 = 9

7 - 9 = 16

If 9 subtracted from 16 leaves 7, then by adding the 9 back again, you should be back to where you started

Question 6

What does 'inverse operation' mean?

Doing the calculation upside down

Making a mistake on purpose

The opposite operation

A medical procedure

The inverse of subtraction is addition, the inverse of addition is subtraction

Question 7

Which calculation could you use to check that 15 + 8 = 23 is correct?

23 + 8 = 15

23 + 15 = 8

15 - 8 = 23

23 - 8 = 15

If a group of 15 and a group of 8 are combined, taking one group away again should leave you with the other

Question 8

How do you know that 20 - 10 = 10?

Because I know 10 + 10 = 20

Because it's a subtraction

Because it's an addition

Because I know about subtraction

Using an addition fact can help to solve a subtraction

Question 9

If 3 + 4 + 10 + 3 = 20, what could you do to check the answer?

Take out all the larger numbers

Use multiplication

Add some extra numbers in too

Add the numbers up again in a different order:

10 + 3 + 3 + 4 or 10 + 4 + 3 + 3

10 + 3 + 3 + 4 or 10 + 4 + 3 + 3

Addition can be done in any order

Question 10

Use number pairs, or bonds, to 20 to find the incorrect calculation:

20 - 13 = 7

20 - 8 = 12

20 - 16 = 14

20 - 2 = 18

16 + 14 gives a total of 30, not 20

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