1) We can see that the ratio of chocolate to cornflakes
is 20:15
But this can be simplified further. The Greatest Common Factor is 5, so:
If we have 20 parts chocolate to 15 parts cornflake, divide
each side by 5 and we get 4:3
This is the ratio of chocolate to cornflakes.
2) We need to work out how much chocolate and cornflakes
we need to make 21 cakes.
The recipe is for 1 cake but we want 21, so multiply both
ingredients by (21 cakes / 1 cake), or simply by 21:
So to make our 21 cakes we need:
 420 g of chocolate
 315 g of cornflakes
Question: If we only had 400g of chocolate, how many
cakes could we make, and what quantity of cornflakes would
we need?
