Rounding numbers

Rounding and Estimation

Rounding whole numbers to the nearest 10

What is Rounding?

Rounding is a way of simplifying numbers. When working with numbers we do not always need to be exact.

We round numbers all the time, without even realising it!

For example, if a friend asked you how much the bag you bought for £12.98 cost, you might say, “it cost about £13”.

When do we use Rounding?

What time is it?

It is almost 12 o’clock Find out more about when rounding is used in BBC videos. http://www.bbc.co.uk/skillswise/topic/rounding-and-estimating

The Rules for: Rounding whole numbers to the nearest 10

1, 2, 3 and 4 get rounded down 5, 6, 7, 8 and 9 get rounded up These rules work for all numbers, whether using tens, hundreds or thousands (or anything else).

Round to the nearest 10 76

49

68

52

97

39

7

25

16

33

92

76

88

58

98

The Rules for: Rounding whole numbers to the nearest 100

1, 2, 3 and 4 get rounded down 5, 6, 7, 8 and 9 get rounded up These rules work for all numbers, whether using tens, hundreds or thousands (or anything else) When rounding to the nearest 100, look at the number to the right e.g. Round 565 to the nearest 100.

The number to the right of the number in the hundreds column is 6. So we round the whole number to the next 100, which is 600

Rounding to the nearest Hundred

147 679 450

Rounding decimals to the nearest whole number

Rules for rounding decimals to the nearest whole number When rounding decimals to the nearest whole number, look at the number to the right of the decimal point.

1, 2, 3 and 4 make the whole number remain the same 5, 6, 7, 8 and 9 require you to round the whole number up Example 45.3 The whole number would be 45 because the number to the right of the decimal point is 3, so the whole number remains the same 45.9 The whole number would be rounded up to 46, because the number to the right of the decimal point is 9, so the whole number is rounded up

When rounding to the nearest whole number :

We think: 5.3 cm is between 5 cm and 6 cm, but it is closer to 5 cm We write: 5.3 cm rounded to the nearest whole number is 5 cm

One of the world's fastest roller coaster reaches speed of 207.81 km / hour.

What is the speed of the roller coaster to the nearest whole number? Place the arrow to the correct position on the number line.

207 207.1 207.2 207.3 207.4 207.5 207.6 207.7 207.8 207.9 208

We think: 207.81 is between 207 and 208, but it is closer to 208.

We write: 207.81 rounded to the nearest whole number is 208.

Extension: Round to the nearest whole number.

56.4 _____

122.6 ____

32.9 _____

106.50 _____

43.2 _____

37.632 _____

345.91 _____

2.09 _____

511.0 _____

60.91 _____

9.7 _____

1789.21 _____

Use rounding to estimate an answer to check your calculation Have a look at this subtraction calculation: 384 - 182 Before - estimate the answer: 384 can be rounded up to 400 and 182 can be rounded up to 200 400 - 200 gives a rough answer of 200

Now do the calculation - remember to start with the units.

After - check the answer makes sense: Estimate: 400 - 200 = 200 Answer: 384 - 182 = 202 - so the answer makes sense!

Estimating Answers

137 + 181 = 318

is about 100

is about 200

the answer is about 300

Estimate the calculations to these sums: Question

191 + 315 127 + 578 504 - 188 97 × 9 3,069 ÷ 9 55 ÷ 11 632 - 128 £15.99 + £19 £4.70 + £12.20 £10 - £2.68 £4.85 × £8 £122.85 ÷ 5

Rounded question

Estimated answer Accurate answer

Round Numbers Assessment Round off the numbers to the nearest 10

675

212

434

557

Round off the numbers to the nearest hundred 234

Complete and round off the sums to the nearest 10

883 - 54 =

678

459 + 32 =

667 - 44 =

912

Complete and round off the sums to the nearest 100

785 - 69 =

558

576 + 12 =

289 - 32 =

Estimate the cost of three items

Functional skills task Use the skills we have practiced to help you solve a real life problemUsing your skills of estimation, approximately how much do you think each item will cost?

Use the Tesco website to find accurate prices: www.tesco.com Item

Estimated cost

Actual cost

Rounded to nearest 10p

Total

Total

Total

A tin of baked beans Two pints of milk A loaf of bread A pack of Sausages A dozen eggs A bar of chocolate Three onions A tin of tomato soup A pair of socks A magazine