7
Find the approximate annual pay of each person.
a Kevin: £270 a week 8
b Malcolm: £1528 a month c David: £347 a week
Gold bars weigh 400 ounces (12.44 kg). On 6 October 2014, one gold bar was worth $413 080. Approximately how much is 1 ounce of gold worth, in dollars?
9
It took me 6 hours 40 minutes to drive from Sheffield to Bude, a distance of 295 miles. My car uses petrol at the rate of about 32 miles per gallon. The petrol cost £3.51 per gallon.
a Approximately how many miles did I travel each hour? b Approximately how many gallons of petrol did I use in driving from Sheffield to Bude?
c What was the approximate cost of all the petrol I used in the journey to Bude and back again?
10
By rounding, find an approximate answer to each of these.
a
462 × 79 0.42
b
e
297 + 721 0.578 − 0.321
f
583 – 213 0.21 12.31 × 16.9 0.394 × 0.216
c
252 + 551 0.78
d
296 × 32 0.325
g
38.3 + 27.5 0.776
h
29.7 + 12.6 0.26
11
Use a calculator to work out the answers to question 10. Round your answers to 3 significant figures and compare them with the estimates you made.
12
A sheet of paper is 0.012 cm thick. Approximately how many sheets will there be in a pile of paper that is 6.35 cm deep?
MR
13
A 5p coin weighs 4.2 g. How many 20-tonne lorries (lorries that can carry 20 tonnes) would be needed to transport a million pounds in 5p coins?
EV
14
The accurate temperature is 18.2 °C. David rounds the temperature to the nearest 5 °C. David says the temperature is about 20 °C. How much would the temperature need to rise for David to say that the temperature is about 25 °C?
15
Use your calculator to complete these calculations. In each case:
i write down the full calculator display of the answer ii round your answer to 3 significant figures. a EV
16
12.3 + 64.9 6.9 − 4.1
b
13.8 × 23.9 3.2 × 6.1
c
48.2 × 58.9 3.62 × 0.042
Here are three calculations. 37.5 × 48.6 21.7 × 103.6 985 ÷ 0.54
a Show that the estimated answer to each of them is the same. b Pete says that the largest actual answer must be to 21.7 × 103.6. Explain why Pete is correct.
c He also says that it is not possible, without doing the full calculation, to say which of the other two has the larger answer. Is Pete correct? Use a calculator to work out which is larger.
1.3 Approximation of calculations
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12/10/14 2:52 PM