Suppose you buy lunch for the drama club. You have enough money to buy 20 salads and 15 sandwiches. The group wants 12 sandwiches. How many salads can you buy?

You can buy 23 salads because the group wants 12 instead of 15 15-12=3

You'd be able to buy 16 salads.

First, you find the ratio for how many salads there are sandwiches:

15:20 = 3:4

Then you set up the ratio next to the current situation:

3:4 = 12:?

Then you're ready to figure it out, if four times three equals twelve sandwiches then we do the same to the number of salads, which is four times four which is ... sixteen.