Sensible rounding Sensible rounding is simply writing or saying answers to questions with a real-life context, so that the answer makes sense and is the sort of thing someone may say in a normal conversation. For example: “The distance from Birmingham to Wolverhampton is 16 miles” is a sensible statement. “The distance from Birmingham to Wolverhampton is 16.3247 miles” is not sensible. “Painting a house takes 6 tins of paint” is sensible. “Painting a house takes 5.91 tins of paint” is not sensible. As a general rule, if it sounds sensible it will be acceptable. When you need to give an answer to a sensible or appropriate degree of accuracy, express it to the same accuracy as the numbers in the question. So, for example, if the numbers in the question are given to 2 signifi cant fi gures give your answer to 2 signifi cant fi gures but remember, unless you are working out an approximation, do all the working to at least 4 signifi cant fi gures or use the calculator display.
Exercise 1E 1
Find approximate answers.
a 5435 × 7.31
b 5280 × 3.211
c 63.24 × 3.514 × 4.2
d 354 ÷ 79.8
e 5974 ÷ 5.29
f 208 ÷ 0.378
2
Use a calculator to work out the answers to question 1. Round your answers to 3 significant figures and compare them with the estimates you made.
3
Round each of the numbers in these statements to a suitable degree of accuracy.
a I am 1.7359 m tall. b It took me 5 minutes 44.83 seconds to mend the television. c My kitten weighs 237.97 g. d The correct temperature at which to drink Earl Grey tea is 82.739 °C. e There were 34 827 people at the test match yesterday. f The distance from Winchester to Andover is 15.528 miles. g The area of the floor is 13.673 m2. 4
By rounding, find approximate answers to each of these.
a
783 – 572 24
b
352 + 675 999
c
3.82 × 7.95 9.9
5
Use a calculator to work out the answers to question 4. Round your answers to 3 significant figures and compare them with the estimates you made.
6
Rewrite this blog, using sensible numbers.
It was a hot day; the temperature was 81.699 °F and still rising. I had now walked 5.3289 km in just over 113.98 minutes. But I didn’t care since I knew that the 43 275 people watching the race were cheering me on. I won by clipping 6.2 seconds off the record time. This was the 67th time it had happened since records first began in 1788. Well, next year I will only have 15 practice walks beforehand as I strive to beat the record by at least another 4.9 seconds.
20
1 Number: Basic number
13810_P008_037.indd 20
12/10/14 2:51 PM