SOLUTION: Pipe A fills the pool in 8 hours, pipe B fills the pool in 12 hours. If pipe A runs for 90 minutes, then pipe B is turned on , how long will it take to fill the pool?

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Pipe A fills the pool in 8 hours, pipe B fills the pool in 12 hours. If pipe A runs for 90 minutes, then pipe B is turned on , how long will it take to fill the pool?       Log On


   

Question 938939: Pipe A fills the pool in 8 hours, pipe B fills the pool in 12 hours. If pipe A runs for 90 minutes, then pipe B is turned on , how long will it take to fill the pool?
Answer by macston(5194) About Me  (Show Source):
You can put this solution on YOUR website!
Pipe A fills 1%2F8 pool per hour.1%2F8*100%=12.5% per hour
Pipe B fills 1%2F12 pool per hour.1%2712*100%=8.3% per hour
Convert the 90 minute fill time to hours:
90+minutes%2F%2860+minutes%2Fhr%29=1.5 hour
Pipe A fills 12.5% of pool/hr x 1.5 hours=18.75% of pool
Together Pipes A and B fill (12.5%+8.3%)=20.8% of the pool per hour.
After 1.5 hours of just Pipe A, 100%-18.75%=81.25% is left to fill.
81.25% of the pool/20.8% per hour (both Pipes)=3.9 hours to finish filling.
1.5 hours(just Pipe A) + 3.9 hours(both Pipes)=5.4 hours total to fill pool.