2. Addition and subtraction

Lesson

Do you remember how to round numbers ?

The number 379 is plotted on the number line.

Round 379 to the nearest 100 and plot it on a number line.

Worked Solution

Idea summary

To round a number to the nearest 100, plot it on a number line and choose the multiple of 100 that it is closest to.

Let's see how we can estimate the answer to a subtraction problem, and an addition problem.

We want to estimate the answer to 258-26.

a

Round each of the two numbers to the nearest and then subtract them.

Worked Solution

b

Find the value of 258-26.

Worked Solution

Idea summary

If we don't need an exact answer to a problem, we can use estimating to find out a close-enough answer. We can also use estimating to check our answers, so it is a great skill to learn.