Flashcards
Percentages and Ratio
Cards in this deck (10)
- 1How to work out Percentage increasework out the difference (increase) between the two numbers you are comparing. Then: divide the decrease by the original number and multiply the answer by 100.
- 2How to work out Percentage decreasework out the difference (decrease) between the two numbers you are comparing. Then: divide the decrease by the original number and multiply the answer by 100.
- 3How to work out reverse percentageExample: A radio sells for £63, after a 40% increase in the cost price tart with the original amount as 100%. We know that the selling price is £63, so 140% = £63. Now calculate 1%:
140% = £63
1% = £63/140
1% = £0.45
The cost price is 100%, so multiply £0.45 by 100.
Cost price = 0.45 × 100 = £45. - 4How to work out compound interestYou deposit £400 in to a bank account paying 5% simple interest per year. How much interest would you have earned after 3 years?
Example: First we need to find 5% of £400.
10% of £400 = £40 so 5% is £20.
As the bank pays simple interest this amount stays the same. So after 3 years you will have earned 20 + 20 + 20 = £60. - 5How to work out RatioThe ratio of girls to boys is 15:12
However, both sides of this ratio are divisible by 3
Dividing by 3 gives 5:4
5 and 4 have no common factors (apart from 1).
So the simplest form of the ratio is 5:4
This means there are 5 girls in the class for every 4 boys. - 6Writing a ratio in the form 1:n or n:1Example: if we are asked to write the ratio 2:5 in the form 1:n, we need to make the left-hand side of the ratio equal to 1. We do this by dividing both sides of the ratio by 2.
2:5 = 2/2 : 5/2
= 1 : 2.5 - 7Writing a ratio in the form 1:n or n:1 2Example: If we were asked to write 2:5 in the form n:1, we would need to make the right-hand side equal to 1. So we would divide both sides by 5:
2:5 = 2/5 : 5/5= 0.4 : 1 - 8Dividing in a ratioExample: Share £200 in the ratio 2:3
This means share the money into 5 equal parts and give one person 2 shares, and the other 3
So 200/5 = 40, one person gets 2 x £40 = £80 and the other 3 x £40 = £120
Check that this adds up to the total, in this case £200 - 9Direct proportionTwo quantities are in direct proportion when they increase or decrease in the same ratio. For example, you could increase something by doubling it, or decrease it by halving.
- 10Direct proportion 2Example: 12 pencils cost 72p. Find the cost of 30 pencils.
72 ÷ 12 = 6
So 1 pencil costs 6p. Now we need to know the cost of 30 pencils. We multiply 6p by 30.
6 × 30 = 180p.
So 30 pencils cost £1.80.
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- Flashcards on Percentages and Ratio, created by chickenshema41 on 24/01/2016.
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