Old McDonald purchased a pool with a capacity 100 gallons for his farm. One day, at 1:00 p. m., he placed a hose onto the pool which filled it with water at a rate of 5 gal per hour. After 10 hours, horses and cows started drinking the water at a rate of 2 gal/hr. Five hours after that, Mr. McDonald noticed the animals and placed a second hose in the pool which filled it at a rate of 4 gal/hr. When did Mr. McDonald have himself a pool full of water?

If it's hours total, then 20 hours total to fill.

Step-by-step explanation:

If it was filled 5 gallons an hour for 10 hours, 5 times 10=50

So there's 50 gallons out of the 100 gallons filled before the animals drank

If the animals drank 2 gal/h with it still being filled at 5 gal/h FOR 5 HOURS, you subtract the 25 (5 gal/h times 5 hours) by 10 (2 gal/h times 5 hours) to get how much gallons were filled in that time span, which is 15

Since he added a hose that filled at 4 gal/h, you can infer that, in total, it is now 9 gal/h because you add 5+4.

The animals are still going to drink at 2 gal/h, so you subtract 9 from 2 and get 7 gallons filling up the pool per hour.

Since you have 35 gallons left (you already filled 65 gallons), you can divide the 35 by 7 to get 5 hours.