Question

the directions for mixing water and powdered milk say that one should use 3 cups of water for each cup of powdered milk. how many cups of powdered milk are needed if 5 cups of water are used

Answer 1

Set up conversion problems so that you can cancel out units that you don't want and introduce units that you do want for your final solution.

5w(m/3w)=15m

So you will need 15 cups of milk if 5 cups of water are used.