A fill pipe can fill a tank in 20 hours, a drain pipe can drain a tank in 30 hours. If a system of n pipes (fill pipes and drain pipes put together) can fill the tank in exactly 5 hours, which of the following are possible values of n (More than one option could be correct)?
(1) 23
(2) 44
(3) 29
(4) 42
a) 1 and 2 only
b) 1 and 3 only
c) 2 and 4 only
d) 2 and 3 only 23.
Sol:
2 fill pipes cancel out 3 drain pipes. Plus, you need an additional 4 fill pipes fill the tank in 5 hours. so the answer has to be 5k + 4.
Both 44 and 29 are possible.
