Estimation & Inverse Operations
Maths: Year 3 & 4 National Curriculum, topic 5.2.3
Checking Answers with Estimation and Inverse Operations
We can use estimation and inverse operations to check our answers are correct.
Example
- Let’s use the same calculation for both estimating and inverse.
- 5,463 + 2,943 = ?
Estimation
- To estimate the answer, we use rounding to help us:
- 5,463 5,500
- 2,943 3,000
- 5,500 + 3,000 = 8,500
- This means we should expect our answer to be around 8,500.
Addition and subtraction
- Let's say we get the answer:
- 5,463 + 2,943 = 8,306
- Let's use the inverse to check:
- 8,306 - 2,943 = 5,363
- We should have gotten 5,463, so this means our answer is NOT correct.
- The answer is actually 8,406.