Chapter 16 Ratio And Proportion Worksheet - Bbc Active Page 9
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1116.5 Using inverse proportion
Example 8
It takes 3 cleaners 6 hours to clean a school.
Work out how long it would take 9 cleaners to clean the school.
3 cleaners take 6 hours.
Examiner’s Tip
Divide the new number of cleaners by the original
9 3 3
number of cleaners. The original number of
Think about the problem: if
cleaners has been multiplied by 3 (3 3 9).
there are more people then the
work should take less time.
6 3 2
Divide the number of hours by 3.
9 cleaners would take 2 hours.
Check: 3 6 18 and 9 2 18.
Example 9
It takes 3 men 2 days to build a wall.
Work out how long it will take 2 men to build the wall.
3 2 6
1 man would take 6 days to build the wall.
6 2 3
There are now 2 men so divide by 2.
2 men will take 3 days.
Check: 3 2 6 and 2 3 6.
Exercise 16F
D
It takes 10 men 2 days to cut a hedge.
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AO 3
Work out how long it will take to cut the hedge if there are:
a
5 men
b
4 men.
5 computers process a certain amount of information in 10 hours.
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AO 2
A O 3
Work out how long it will take 25 computers to process the same amount of information.
A factory uses 3 machines to complete a job in 15 hours.
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AO 2
A O 3
If 2 extra machines are used, how long will the job take?
It takes 6 machines 3 days to harvest a crop. How long would it take 2 machines?
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AO 2
A O 3
A large ball of wool is used to knit a scarf.
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AO 2
A O 3
The scarf is 40 stitches wide and 120 cm long. If the same size ball of wool is used to knit a scarf 25
stitches wide, work out the length of the new scarf.
A document will fi t onto exactly 32 pages if there are 500 words on a page.
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AO 2
A O 3
If the number of words on each page is reduced to 400, how many more pages will there be in the
document?
271
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