Lesson

Do you remember how to round numbers to the nearest 10,\, 100, or 1000?

Round 936 to the nearest ten.

Worked Solution

Idea summary

When rounding a number to the nearest 10:

Use a number line to check if it is closer to the ten above, or the ten below the number.

If a number is exactly in the middle, round to the higher number.

How can we estimate the answer to an addition or subtraction problem?

Look at the number sentence:

6266-143=⬚

a

6266-143 will be in the:

A

6200s

B

6100s

C

6000s

Worked Solution

b

Find the value of 6266-143.

Worked Solution

Idea summary

Rounding can assist us in estimating an answer to a number problem as we don't always need to determine the precise solution.

We can also estimate our answer to multiplication and division problems. In fact, the process is not that different to addition and subtraction. Let's see how, in this video.

Let’s estimate the solution to 24 \times 24 by rounding the digits first.

a

Rewrite the calculation but use rounded numbers to the nearest 10.

Worked Solution

b

Calculate 20 \times 20.

Worked Solution

c

Is 400 going to be larger or smaller than the actual result of 24 \times 24?

Worked Solution

Idea summary

Same with the process of addition and subtraction, we don't always need to work out the exact answer to a number problem, so rounding can help us estimate an answer. This means we can check that our answer seems reasonable.

Use estimation and rounding to check the reasonableness of answers to calculations.