We will find the amount used in a shower lasting 5 minutes as follows:
*First, we write the equation of proportionality:
Here w is the amount of water, t is the time it takes per shower and k is the constant of proportionality. Using the first set of information we solve for k:
Now, that we know the value of k, we determine the amount of water that will be used on a 5 minutes shower:
So, they will use 2.5 gallons of water.