1. Targeting Grade C GCSE Mathematics Number
Unit 4 Percentages and Interest

2. Can you: If not you need Find percentages of amounts
Find percentage increase or decrease
Try a test
Find simple interest
Find compound interest
TOP: Review how to find simple percentages
Practice 1: Splitting percentages up
Practice 2: Finding percentage increase and decrease
TAIL 1
Practice 3: Finding simple interest
Practice 4: Finding compound interest
TAIL 2
If not you need

3. TOP: Solve these simple percentage questions.
Find 10% of £20
Find 50% of £100
Find 30% of £60
Find 70% of £120
Find 75% of £200
Remember to split the amount into 10% (by dividing by 10) and then multiply by the number of 10s you need!
Lesson

4. Practice 1: Solve these percentage problems.
Find 35% of £120
Find 83% of £250
Find 12% of 75kg
Find 17 ½% of 70 miles
Find 24% of £65.50
Split your percentage into parts like 10%, 5%, 2 ½% and 1%
Remember to find 10%, then
1% (by dividing your 10% by 10),
or 5% (by dividing your 10% by 2),
or ½% (by dividing your 1% by 2),
or 2 ½% (by dividing 5% by 2.
Lesson

5. Practice 2: Find these percentage increases.
Increase £100 by 15%
Increase 85kg by 12 ½%
Increase 754 m by 68%
Find these percentage decreases.
Decrease £100 by 75%
Decrease 65 miles by 34%
Decrease 378 km by 7 ½%
One way to increase or decrease amounts by percentages is to find the percentage and then add (to increase) or subtract (to decrease)
Lesson

6. TAIL 1 Are you ready for the answers ?
The selling price of a computer is the list price plus VAT at 17 ½ %. The list price of a computer is £786.
Work out the selling price of the computer.
(1) 17 ½ /100  786 =
= £923.55
(2) 60/100  5300 = £3180
(2) Work out 60% of 5300 kg.
(3) Frances sees three different advertisements for jeans.
Bob’s – 15% off £ Disco’s – ⅔ of £36 Sanjay’s – £ ½% VAT
Work out the cost of the jeans in each advertisement.
(a) Bob's (b) Disco's (c) Sanjay's
(3) (a) 15/100  30 = £4.50
30 – 4.50 = 25.50
(b) 2/3  36 = £24
(c) 17.5/100  = £25.80
Lesson

7. Practice 3: Find the simple interest for the following:
£60 for 2 years at 4% interest per annum
£150 for 3 years at 7.5% interest per annum
£5000 for 6 years at 3% p.a.
£2500 for 10 years at 12.5% p.a.
£750 for 5 years at 6.5% p.a.
Find the interest for one year then multiply by the number of years!
Lesson

8. Practice 4: Find the compound interest for the following:
£150 for 2 years at 7% p.a.
£500 for 3 years at 12% p.a.
£7500 for 3 years at 3.5% p.a.
£65 for 2 years at 5% p.a.
£2500 for 4 years at 6.5% p.a.
Remember the formula (1+(percentage  100))number of years to help you e.g. for (1) do
£150  (1.07)2
Lesson

9. TAIL 2
(1) Yesterday Simon repaired a computer and charged a total of £ Simon reduces his charges by 5% when he is paid promptly. He was paid promptly for yesterday's work on the computer.
  Work out how much he was paid.
(2) Jane is going to buy a computer for £ ½ % VAT. Work out the total price, including VAT, that Jane will pay for the computer.
(3) Find the simple interest on £2500 invested for 2 years at 6% per year.
(4) £5000 is invested for 3 years at 4% per annum compound interest. Work out the total interest earned over the three years.
Work out the simple interest on £530 at 4.5% per annum after 3 years.
(1) 5/100  =
– =
= £255.84
(2) 17 ½ /100 
= = £564
(3) 6/100  2500 = 150
“150”  2 = £300
(4)  5000 = £
(5) 4.5/100  530 = 23.85
“23.85”  3 = £71.55
Are you ready for the answers ?
Lesson