Example

Here is an example of the maths you will need to learn for this unit

Estimation

To estimate calculations you round your numbers to 1 significant figure and then perform the calculation. For example, if you need to calculate 456 x 34

• Find the first non-zero digit.

  • In 456, that’s the 4.

  • In 34, that’s the 3.
     

• Look at the next digit to the right.

  • For 456, look at the 5 (the second digit).

  • For 34, look at the 4 (the second digit).
     

• Decide whether to round up or keep the same.

  • If that “next digit” is 5 or more, round the first digit up by 1.

  • If it’s 4 or less, keep the first digit the same.
    So for 456, the 4 gets rounded up to 5  and for 34, the 3 stays the same
     

• Replace every digit after your first one with zeros (or drop them if you’re in the decimals).

  • After rounding, any digits to the right become zeros (for whole numbers), or you drop them (for decimals).

  • So 456 becomes 500 and 34 becomes 30

  • Now we can do the much easier calculation
    500 x 30 = 15,000

Have a try yourself with the quiz below

Quick Mental Estimation Quiz

Round each number to 1 s.f. and multiply or divide to get your estimate.