Learn how to estimate calculations
Estimations are used to quickly estimate the answer of an expression.
Example
134+159≈130+160≈290
You look at the last digit in each number
If the last number is < 5, then round off to the nearest 0
If the last number is ≥ 5, then round off to the nearest 10
You can estimate products and quotients as well.
Example
Round off the factors and multiply the factors.
55.87.42→567=8
55.8≈56
7.42≈7
Example
Multiply the two decimal numbers.
First we multiply the two numbers without estimating this to be able to compare the different results.
3.5⋅7.3=x3.5⋅7.3_105+2450_25.55
Now if we would have estimated the answer instead we would have round off 3.5 to 4 and 7.3 to 7. This would have given us an estimate of
3.5⋅7.3≈4⋅7=28
As we can see the answers are pretty similar, but not identical.
Video lesson
Estimate