Question

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. At what time and (am / pm) did Mr. McDonald have himself a pool full of water?

Answer 1

10 hours : 10*5 = 50 gallons

15 hours: amount in pool + hose * 5 hours - drinking*5 hours

      = 50 +5*5 - 2*5 = 50+25-10  = 65 gallons

100 = amount in pool + 1st hose*hrs - drinking*hrs + 2nd hose*hrs

hrs is after the 15 hours already filling the pool

100 = 65 gallons + 5*h -2h +4h

combine like terms

100 =65 +7h

subtract 65

35 = 7h

divide by 7

h=5

add the 15 hours before

20 hours to fill the pool

1pm + 20 hrs

24 hrs would be 1pm again so subtract 4 hours

9 am the next day