David wants to find out how many gallons of water he has drank in he past 7 hours. He drinks 3/4 liters every 1/2 hour. How much has he drank?

Answer 1

Hello Matthew,

You can set up proportions with gallons of water on top, hours at the bottom:

gallons of water 3/4 X

________________ ____ = ______

hours 1/2 7

We're looking for x because the problem asks how many gallons has David drank over 7 hours.

We'll cross multiply: 7 * 3/4 = x * (1/2)

Divide both sides by 1/2: 7*(3/4)/(1/2) = x

You are dividing by 1/2, that means you can MULTIPLY by 2/1: 7*(3/4)*(2/1) = x

7*(6/4) = x

7*(3/2) = x

21/2 = x so x = 10.5 gallons or 10 1/2 gallons

Answer: David has drank 10 1/2 gallons of water in the past 7 hours.