Bunuel wrote:
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 hours. If pipe A was opened at 8:00 am and Pipe B at 9:00 am, at what time will the pool be full?
A. 15:00
B. 17:00
C. 18:00
D. 19:00
E. 20:00
let t=time to fill pool
at 9am pool is 1/6 full
rate of A-B=1/12
t(1/12)=5/6
t=9 hours
9am+9 hours=18:00
C
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