Problem: Each valve , , and , when open, releases water into a tank at its own constant rate. With all three valves open, the tank fills in hour, with only valves and open it takes hours, and with only valves and open it takes hours. The number of hours required with only valves and open is
Answer Choices:
A.
B.
C.
D.
E.
Solution:
Let , and denote the number of tankfuls of water delivered by valves , and respectively in one hour. Then
.
Sabtracting the sam of the last two equations from twice the first, gives so that tankful will be delivered by valves and in hours