Targeting Grade C

Number

Unit 4 Percentages and Interest

GCSE Mathematics

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

Can you:

•Find percentages of amounts

•Find percentage increase or decrease

Try a test

•Find simple interest

•Find compound interest

Try a test

If not you need

TOP: Solve these simple percentage questions.

(1) Find 10% of £20

(2) Find 50% of £100

(3) Find 30% of £60

(4) Find 70% of £120

(5) Find 75% of £200

Lesson

Remember to split the amount into 10% (by dividing by 10) and then multiply by the number of 10s you need!

Practice 1: Solve these percentage problems.

(1) Find 35% of £120

(2) Find 83% of £250

(3) Find 12% of 75kg

(4) Find 17 ½% of 70 miles

(5) Find 24% of £65.50

Lesson

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.

Split your percentage into parts like 10%, 5%, 2 ½% and 1%

Practice 2: Find these percentage increases.

(1) Increase £100 by 15%

(2) Increase 85kg by 12 ½%

(3) Increase 754 m by 68%

Find these percentage decreases.

(4) Decrease £100 by 75%

(5) Decrease 65 miles by 34%

(6) Decrease 378 km by 7 ½%

Lesson

One way to increase or decrease amounts by percentages is to find the percentage and then add (to increase) or subtract (to decrease)

Are you ready for the answers ?

TAIL 1

Lesson

(1) 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.

(2) Work out 60% of 5300 kg.

(3) Frances sees three different advertisements for jeans.

Bob’s – 15% off £30 Disco’s – ⅔ of £36 Sanjay’s – £22 + 17 ½% VAT

Work out the cost of the jeans in each advertisement.

(a) Bob's(b) Disco's (c) Sanjay's

(1) 17 ½ /100 786 = 137.55

137.55 + 786 = £923.55 (2) 60/100 5300 = £3180

(3) (a) 15/100 30 = £4.50

30 – 4.50 = 25.50

(b) 2/3 36 = £24

(c) 17.5/100 22 + 22 = £25.80

Practice 3: Find the simple interest for the following:

(1) £60 for 2 years at 4% interest per annum

(2) £150 for 3 years at 7.5% interest per annum

(3) £5000 for 6 years at 3% p.a.

(4) £2500 for 10 years at 12.5% p.a.

(5) £750 for 5 years at 6.5% p.a.

Lesson

Find the interest for one year then multiply by the number of years!

Practice 4: Find the compound interest for the following:

(1) £150 for 2 years at 7% p.a.

(2) £500 for 3 years at 12% p.a.

(3) £7500 for 3 years at 3.5% p.a.

(4) £65 for 2 years at 5% p.a.

(5) £2500 for 4 years at 6.5% p.a.

Lesson

Remember the formula (1+(percentage 100))number of years

to help you e.g. for (1) do

£150 (1.07)2

TAIL 2 (1) Yesterday Simon repaired a computer and

charged a total of £269.30. 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 £480 + 17 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.

(5) Work out the simple interest on £530 at 4.5% per annum after 3 years.

Lesson

(1) 5/100 269.30 = 13.465

269.30 – 13.465 =

255.835 = £255.84

(2) 17 ½ /100 480 + 480

= 84 + 480 = £564 (3) 6/100 2500 = 150

“150” 2 = £300 (4) 1.043 5000 = £5624.32 (5) 4.5/100 530 = 23.85

“23.85” 3 = £71.55

Are you ready for the answers ?