Question

A tank is being filled with water using an old

Answer 1

Found a similar problem with the given table. 

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

Because the interval is every 10 minutes, we will use 10 and multiply it to each rate and get the sum total.

42*10 + 40*10 + 38*10 + 35*10 + 35*10 + 32*10 + 28*10 + 20*10 + 19*10 + 10*10
420 + 400 + 380 + 350 + 350 + 320 + 280 + 200 + 190 + 100
2,990

There will be a total of 2,990 gallons in the tank after 90 minutes.