Gcse maths: more ratios

If you know the ratio between parts and the actual size of one part, you can scale the ratio up to find the other parts.

Put into practise 1 : Mortar is made from sand and cement in the ratio 7:2 if 21 buckets of sand are used, how much cement is needed?

You need to multiply by 3 to go from 7 to 21 in the left hand side - so do that to both sides.
7:3 X 3 21:6
So 6 buckets of cement are needed.

Practise 2: Mrs miggins owns tabby cats and ginger cats in the ratio 3:5 all her cats are either tabby or ginger, and she has 12 tabby cats. How many cats does Mrs Miggins have in total?

Multiply both sides by 4 to go from 3 to 12 on the LSH = 12:20
So Mrs Miggins has 12 tabby cats and 20 ginger cats. So in total she has 12 + 20 = 32 cats.

Practise: Jess, Mo and Greg share £9100 in the ratio 2:4:7. How much does Mo get?

1) Add up the parts: the ratio 2:4:7 means there will be a total of 13 parts.

2) Divide to find one "Part": Just divide the total amount by the number of parts - £9100 / 13 = £700 (=1 part)

3) Multiply to find the amounts: We want to know Mo's share which is 4 parts
4 parts = 4 X £2800