Practice associating the area under rate-of-change curves with net change.

Problem

Firemen use one hose to spray water on a house fire at a rate of 12 gallons per minute. After 20 minutes, the firemen connect a second hose to a hydrant to double the total spray rate. It takes 100 minutes to put out the fire. The graph below shows the spray rate as a function of time.
How much water do the firemen use to put out the fire?
  • Your answer should be
  • an integer, like 6
  • an exact decimal, like 0, point, 75
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
gallons