Answer:
The pump should be added by 8PM
Step-by-step explanation:
An oil tanker can be emptied by the main pump in 4 hours.
An auxiliary pump can empty the tanker in 11 hours.
the main pump is started at 7 PM,and we have 10 PM - 7PM = 3 hours to empty the tank.
So we have to look for the combined rate of the both pumps .
Let's say the volume= x
Rate of first pump= x/4
Rate of second pump= x/11
The rate will be added together
Combined rate= x/11 + x/4
Combined rate= 15x/44
But they have three hours to complete their pump
15x/44 = 3
X=1.0227
The pump should be added by 8PM
