Using inverse calculations
What is an inverse calculation?
An inverse calculation uses the opposite operation to check whether the answer is correct.
For example: If we add 81 + 29 is the total 100 or 110?
We can check the answer by subtraction
+29 or + 29
Work out these subtractions to check which answer was correct. We should end up with 81 if the answer is correct.
- 29 - 29
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Which answer was correct?
That's right 81 + 29 = 110
When checking using the inverse
110 - 29 = 81
Can you see that we have the same numbers in both addition and subtraction?
This is how we know the answer is correct.
Once you have worked out the answers complete the inverse calculations below to check.
1. ???? 2. ???? 3. ???? 4. Complete
+ 5004 + 3153 + 2044 + this inverse
8017 6276 8068 independently
Once you have worked out the answers complete the inverse calculations to check. (Write the inverse calculation underneath the subtraction like above.)
Once you have finished use the inverse to check your answers.