Rounding Numbers

Today we will be learning: how to round numbers up or down to the nearest 10 how to estimate answers.

Mental Activity We are going to play “Fizz-Buzz”. Here are the rules. Count in ones. If you reach a multiple of 5, say “Fizz” instead of the number. If you reach a multiple of 10, say “Fizz-Buzz” instead of the number.

Try counting backwards. Start on 12 Now start on 56 Try counting backwards. Start on 39

Today we are going to learn about rounding numbers to the nearest 10. Main Activity Today we are going to learn about rounding numbers to the nearest 10.

How many jumps away is this number from the nearest multiple of 10? 2 8

20 28 30 Is 28 nearer to 20 or 30? 30

40 28 is nearer to 30, so when we round it, we round up to 30. What about 42? Would you round it up to 50 or down to 40? 40 50 42 40

Round these numbers up or down to the nearest multiple of 10. 63 79 56

What are the rules for rounding numbers up or down? Let’s look at a“Top Tip” to find out. What happens if the units digit is a 5?

Top Tip If the units digit is below 5, round the number down to the nearest multiple of 10. If the units digit is 5 or above, round the number up to the nearest multiple of 10.

We can use rounding to help us to estimate when adding two numbers. 43 + 59 43 can be rounded to 40. 59 can be rounded to 60. 40 + 60 = 100 We have estimated the answer to the nearest 10.

Let’s try estimating some more answers. 51 + 42 = Estimate Answer 90 93

Try this one… 46 + 31 = Estimate Answer 80 77

Let’s use rounding and estimating to help us with a word problem. In one class there are 28 children and in another there are 31 children. How many children are there altogether? Estimate Answer 60 59

Group Work Rounding using number lines. Rounding to multiples of 10. Rounding to estimate answers when adding two two-digit numbers.