Using estimation to check answers

​​In a nutshell

Estimation involves finding an approximate answer for a calculation so you can have an idea that the real answer is correct. The main method of estimation is to round numbers in a calculation to make it faster and easier to perform the calculation.

Estimating

When estimating a calculation, round the numbers so they are easier to handle. Round the numbers to the first digit, then the calculation should be easier to perform. To represent an estimation, use the symbol $$(\approx)$$ which means "approximately equal to".

Example 1

Estimate $$612 \times 11$$.

First, round $$612$$.

$$612 \approx 600$$​

Then, round $$11$$.

$$11 \approx 10$$​

Attempt the calculation with the rounded numbers. 

​$$600 \times 10 = 6000$$​

Therefore,

$$\underline{621 \times 11 \approx 6000.}$$

Note: You may not need to round every number in a calculation as long as you are still able to estimate a calculations.  

Example 2

Estimate $$7141- 3987$$.

Round $$7141$$ and $$3987$$ using the first digit. 

​

$$7141 \approx 7000 \\3987 \approx 4000$$

Estimate the answer.

​

​$$7000-4000 =3000$$

Therefore,

​$$\underline{7141-3987 \approx 3000.}$$​​