A tank is being filled with water using a pump that is old and slows down as it runs. The table below gives the rate at which the pump pumps at
ten-minute intervals. If the tank is initially empty, approximate how much water is
in the tank after 90 minutes?
Elapsed time
(Minutes) 0 10 20 30 40 50 60 70 80 90
Rate
(gallons / minute) 42 40 38 35 35 32 28 20 19 10

Question

A tank is being filled with water using a pump that is old and slows down as it runs. The table below gives the rate at which the pump pumps at
ten-minute intervals. If the tank is initially empty, approximate how much water is
in the tank after 90 minutes? 
Elapsed time
(Minutes) 0 10 20 30 40 50 60 70 80 90
Rate
(gallons / minute) 42 40 38 35 35 32 28 20 19 10

dumbcow · Answer

#gallons = rate*time

If we assume a constant rate between intervals then total gallons is:
$$\sum_{i=1}^{10} r_i t$$
---> 42*10 + 40*10 .... + 10*10