Number
Percentages
Examples
A notepad costs £1
25%() of £1 = 25p
£1 – 25p = 75pThe sale price of the notepad is 75p
A CD normally costs £10
25% of £10 = £2.50
£10 - £2.50 = £7.50The reduced price of the CD is £7.50
Exercise 1
1.A pack of envelopes costs £1
50% of £1 = ……….p
£1 - ……. = ……….pThe sale price of the envelopes is ……….p
2.A plant costs £10
50% of £10 = £……….
£10 - ……. = £ ……….The sale price of the plant is £……….
3.A pack of Christmas cards costs £1
75% of £1= ……….pYou will have saved ……….p
4A bottle of aftershave costs £10You will save £ ……….
You earn £100 per week.
If you had a pay rise of 25% then you would get an extra 25p for each £1 you earn.
As you earn 100 x £1 you will get 100 x 25p extra.
100 x 25p = 2500p (£25.00)
If you had a pay rise of 50% then you would get an extra 50p for each £1 you earn.
100 x 50p = 5000p(£50.00)
You have a pay rise of 10%
100 x 10p = 1000p (£10.00)
5.You have a pay rise of 20%
100 x …… p = ……..p (£……..)
6.You have a pay rise of 5%
100 x …… p = ……..p (£……..)
7.You earn £300 per week. Then you have a pay rise of 10%.
300 x …… p = ……..p (£……..)
8.You earn £200 per week. Then you have a pay rise of 20%
……. x ……p = ..……p (£……..)
Let’s forget the £s for the moment and just use the rule.
Remember – multiply the number by the % then divide by 100.
Examples
Find 10% of 250
250 x 10 ÷ 100
Step 1:250 x 10 = 2500
Step 2:2500 ÷ 100 = 25
Answer:10% of 250 is 25
Find 5% of 340
340 x 5 ÷ 100
Step 1:340 x 5 = 1700
Step 2:1700 ÷ 100 = 17
Answer:5% of 342 is 17
9.Find 10% of 400
400 x 10 = ……..…….. ÷ 100 = ……..10% of 400 is ……..
10.Find 5% of 700
700 x …….. = ……..…….. ÷ 100 = ……..5% of 700 is ……...
11.Find 5% of 200
……………………….……………………………………………...
12.Find 10% of 200
……………………….……………………………………………...
Exercise 1
Look at these strips which are partly coloured in black.
A /B
C
D
13.Strip A is ......
14.Strip B is ......
15.Strip C is ......
16.Strip D is ......
Of 100 people asked about their drinking habits:
46 drank alcohol at weekends only
23 drank alcohol 3 days a week
15 drank alcohol 4 days a week
10 drank alcohol every day
Remember 1 person = 1% here because there are 100 people altogether.
Complete these statements with a number, choosing from:- 5, 25, 35, 50
17.Less than% only drank at weekends
18.More than% drank every day
19.About% drank 3 days a week
20.Less than% drank more than 3 times a week.
A year later the figures were very similar but 50% of those who drank alcohol every day had stopped drinking altogether.
21.How many people now drink alcohol every day?
22.What % is this?
23.What % of people now drink alcohol at weekends only or not at all?
Study the following calculations and try to understand what is happening.
To work out 10% of 900
10% = 900 x = 90
To work out 20% of 900
20% = 900 x = 180or2 × 10% of 900
therefore 90 x 2 = 180
To work out 5% of 900
5% = 900 x = 45or of 10% of 900
therefore = 45
To work out 1% of 900
1% = 900 x = 9or of 10%
therefore = 9
And just a few more:
To work out 50% of 900
50% = 900 x = 450or of 100%
therefore = 450
To work out 25% of 900
25% = 900 x = 225or of 100%
therefore = 225
To work out 75% of 900
75% = 900 x = 675or50% + 25%
therefore 450 + 225 = 675
So to sum up:
To find 50% - you can find
To find 25% - find then
To find 75% - find 50% and 25% and add them together.
10% = 20% = 2 x 10%30% = 3 x 10%5% = of 10%
or you can use the formula
number x % ÷ 100e.g. 20% of 300 300 x = 60
You may find that you use different methods in different situations.
Examples
15% of 300 = 300 x 15 ÷ 100 = 4518% of 50 = 50 x = 9
Exercise 2
- 10% of 300 shirts
- 75% of 12 kg
- 30% of 30 kg
- 5% of 1000 ml
The price of a second hand car has decreased by 20% from £1500. What is it worth now?
20% of £1500 = 1500 x 20 ÷ 100 = £300
As it is a decrease:
£1500 - 300 = £1200
If the car had increased by 20%, it would be
£1500 + 300 = £1800.
Another second hand car has also decreased by 20% but the original value was £3500.
As it has decreased
£3500 – (3500 x 20 ÷ 100) = £2800
If the car has increased by 20%, it would be
£3500 + (3500 x 20 ÷ 100) = £4200
5.Spud-U-Buy does party packs at a discount (decrease).
100 spuds at a 10% discount
200 spuds at a 20% discount
Spud-chilli cost 85p each
Spud-cheese cost 75p each
Spud-salad cost 70p each
a)Calculate the cost of 100 spud-chillis. Work out the discount. What will they cost after the discount is removed?
b)Calculate the cost, after discount, of 200 spud-salads.
c)Calculate the cost, after discount of 50 spud-cheeses and 150 spud-chillis (discount of 20%)
6.An employee earning £190 a week is offered an increase of either £13·50 or 7%. Which one would you take?
7.The cost of a package holiday for an adult is £574. It is 70% of that for a child. Find the cost of 1 adult and 1 child.
8.The cost of an £8000 car goes up by 2%. What will its new cost be? What is the deposit of 10% on the new car?
Workbook 7Level 1: Numeracy/Application of Number© West Nottinghamshire College 2004
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