Grades 1 and 2 | Math | Elementary School | Checking Calculations with Inverse Operations

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Math: Elementary School: 1st and 2nd Grade Quiz - Checking Calculations with Inverse Operations (Questions)

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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!

Can you check the calculations by adding in a different order or by using the inverse operation?

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

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

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

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

[ ]	20 - 13 = 7
[ ]	20 - 8 = 12
[ ]	20 - 16 = 14
[ ]	20 - 2 = 18

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

[ ]	20 - 10 = 20
[ ]	20 - 0 = 20
[ ]	20 - 15 = 5
[ ]	20 - 19 = 1

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

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

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

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

10.

What does 'inverse operation' mean?

[ ]	Doing the calculation upside down
[ ]	Making a mistake on purpose
[ ]	The opposite operation
[ ]	A medical procedure

Math: Elementary School: 1st and 2nd Grade Quiz - Checking Calculations with Inverse Operations (Answers)

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

[ ]	16 + 9 = 7
[x]	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

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

[ ]	23 + 8 = 15
[ ]	23 + 15 = 8
[ ]	15 - 8 = 23
[x]	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

How do you know that 20 - 10 = 10?

[x]	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

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

[ ]	20 - 13 = 7
[ ]	20 - 8 = 12
[x]	20 - 16 = 14
[ ]	20 - 2 = 18

16 + 14 gives a total of 30, not 20

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

[x]	20 - 10 = 20
[ ]	20 - 0 = 20
[ ]	20 - 15 = 5
[ ]	20 - 19 = 1

20 + 10 would not give a total of 20

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
[x]	Add the numbers up again in a different order: 10 + 3 + 3 + 4 or 10 + 4 + 3 + 3

Addition can be done in any order

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

[ ]	Subtract the numbers in a different order
[x]	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

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
[x]	By adding 23 and 22

Adding the two smaller numbers should give the larger number

How could you check 62 + 38 = 100?

[ ]	By taking away 100
[ ]	By finding the difference between 62 and 38
[ ]	By subtracting 100 from 62
[x]	By subtracting 38 from 100

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

10.

What does 'inverse operation' mean?

[ ]	Doing the calculation upside down
[ ]	Making a mistake on purpose
[x]	The opposite operation
[ ]	A medical procedure

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