Maths Topic 14 - Ratio, proportion & scale

Ratio, Proportion & Scale are maths skills that are commonly tested in 11+ exams and Selective School exams in the UK.

Example Questions

Example Question 1:

Divide 108 in the ratio of 5:4

Answer: 60:48

Explanation: Add together the ratio parts 5 + 4 = 9. Divide 108 by 9 = 12 (as a fraction of the whole 108, ¹/₉= 12). 5 × 12 = 60 and 4 × 12 = 48

Example Question 2:

Hetta, Ruby and Eva divide 250 sweets between them in the ratio of 5:3:2. How many sweets does Ruby receive?

Answer: 75

Explanation: Add together the ratio parts 5 + 3 + 2 = 10 (you are working in tenths). One tenth of the 250 sweets = 25. Ruby receives ³/_10,which is 25 × 3 = 75.

Example Question 3:

Joel wants to make some fresh fruit juice. He uses a recipe that tells him to use 1 lemon to every 3 oranges. If Joel has 21 oranges, how many lemons will he need?

Answer: 7

Explanation: 1 in every 4 fruits used is a lemon or ¼ (this is the proportion). Joel has 21 oranges, which represents ³/₄of the fruit juice, you can find ¹/₄by dividing the 21 by 3 = 7. The lemons were ¹/₄of the fruit juice. Joel will need to use 1 × 7 lemons = 7.