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