Final answer:
To fill all 3 tanks one at a time, it will take 10 hours.
Step-by-step explanation:
To determine the number of hours it will take to fill all 3 tanks one at a time, we need to calculate the net rate at which water is being filled in the tanks.
Each tank is being filled from two pipes, one at a rate of 25,000 gallons per hour and the other at a rate of 45,000 gallons per hour. Since there are 3 tanks, the total incoming rate would be 3 times the sum of the individual rates, which is 3 x (25,000 + 45,000) = 3 x 70,000 = 210,000 gallons per hour.
Water leaves the system at a rate of 60,000 gallons per hour. Therefore, the net rate at which water is being filled in the tanks is 210,000 - 60,000 = 150,000 gallons per hour.
Each tank can hold 1 million gallons and is currently half full, which means it needs to be filled with 500,000 gallons.
So, the number of hours it will take to fill all 3 tanks one at a time can be calculated by dividing the required total amount of water (3 x 500,000 = 1,500,000 gallons) by the net rate at which water is being filled in the tanks (150,000 gallons per hour).
Number of hours = 1,500,000 / 150,000 = 10 hours