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Making-percentages

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Making percentages You use percentages to compare different situations. E.G. John gets 15 out of 20 for his Maths test and 12 out of 15 for his English test. Express these numbers as percentages. Which subject does John do best in? Finding value of a percentage You often see percentages in the newspapers and on the news. You can calculate the value of a percentage if you know the whole. E.G. The fire-fighters get a pay rise of 16%. Kiran earns £16 500 pa at present as a fire person. What is his pay rise in money, and what is his new pay? Reverse percentages Sometimes you are not given the w hole amount, but you are told the value of a percentage. You can then work backwards to find the value of 1% and then the value of any other percentage. E.G. An invoice for £116.33 includes VAT at 17.5%. You have been asked to find the cost before VAT was added.

Ans

part 100  percentage whole
15  100  75% for Maths and 20 12  100  80% for English 15
John does best in English

Ans

percentage  whole  value 100 16  16500  £2640 rise 100
£16 500 + £2640 = £19140 is his new pay

Ans

value given  100  value of 100 % percentage
116 .33  100  £99 100  17 .5

Note how you had to add 100% of the cost before VAT onto the 17.5% VAT to work out what the percentage before VAT was.

Your turn 1) What is 17.5% of £450? Find 2.5% of £14 000 You will get a 6% pay rise. If you earn £70 per week now, what is your new pay? Find 120% of £50 35% of beans is carbohydrate. How many grammes of carbohydrate are there in a standard serving of 250g of beans? 4.6% of men are colour blind but only 0.24% of women are colour blind. If there are 3 000 men and 4 500 women in the College, how many colour blind people are there in College? About 13% of children in the 11 to 15 age range smoked on a regular basis in 1996. If a school has 2 250 pupils in that age range - how many might be expected to smoke? (http://www.ash.org.uk/html/factsheets/html/fact03.html) 8) Find 2.6% of £45.50 6) Your Turn 1) 2) 3) If 5% of an amount of money is £7, work out w hat the w hole sum is If 10% of a sum of money is £12.50, work out what the w hole sum is You have had a 10% pay rise. If your wages are £5.50 per hour after the pay rise, what did you get before the rise? Hint: what percentage is the £5.50 worth? An invoice for some nursery equipment comes to £681.50 including the VAT at 17.5%. You have been asked to 'split out the VAT' and find the cost of the equipment before the VAT was added. A group of students decide to take their long-suffering course tutors to a restaurant after their course finishes. The bill for 25 people comes to £412.50 including a 10% service charge on large groups. What was the bill before the service charge was added? 11.2% of baked beans is carbohydrate. If the carbohydrate in a portion of baked beans in the canteen weighs 15g, how many g does the whole portion weigh?

Your turn 1) 2) Express £2.40 as a percentage of £12. Harjinder gets 23 votes. Jane gets 32 votes. Aaron gets 15 votes. Work out each person's percentage of the votes. Hint: add up all the votes to get the w hole. Find 30cm as a percentage of 1m. 10 out of 111 cats examined in a vet's clinic were infected with Borna Disease Virus (BDV) which can cause symptoms in humans. Express these figures as a percentage. (http://news.bbc.co.uk/1/hi/health/213265.stm) You are paid £3.60 per hour for a Saturday job. After you have been in the job for three months you get a 50p per hour pay rise. Express the rise as a percentage of your hourly rate. First class stamps went up from 27p to 29p recently. Express the price rise as a percentage of the original price.

2) 3) 4) 5)

3) 4)

6)

4)

5)

7)

5)

6) Ans

1) 20% 2) 32.9%, 45.7%, 21.4% 3) 30% 4) 9.0% 5) 13.9% 6) 7.4%

Ans 1) £78.75 2) £350 3) £4.20 4) £60 5) 87.5g 6) 148 7) 292 8) £1.83

ANS 1) £140 2) £125 3) £5 4) £580 5) £375 6) 134g

Kpb 2002 / rev 2

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