文档介绍：LO: To be able to round numbers
Mrs Vivien Criddle
Westfield Middle School
What is rounding?
Sometimes we want to add numbers in our head but the numbers are a bit tricky.
We can estimate (take a good guess) the answer
It is easier if we use numbers that are in 10s
Rounding means we find the nearest 10
Up or Down
1, 2, 3, 4
5, 6, 7, 8, 9
Does the number end in…
Does the number end in…
Round down
Round up
Lets look at a number line…
Where do these numbers go?
21
39
64
83
Let’s take a closer look…
21
Is 21 closer to 20 or 30?
Does it end in 1, 2, 3 or 4?
Round down!
Another close look…
39
Is 39 closer to 30 or 40?
Does it end in 5, 6, 7, 8 or 9?
Round up!
Another close look…
64
Is 64 closer to 60 or 70?
Does it end in 1, 2, 3 or 4?