NandishSS wrote:A draining pipe can empty a pool in 4 hours. On a rainy day, when the pool is full, the draining pipe is opened and the pool is emptied in 6 hours. If rain inflow into the pool is 3 liters per hour, what is the capacity of the pool?
A. 9 liters
B. 18 liters
C. 27 liters
D. 36 liters
E. 45 liters
We can PLUG IN THE ANSWERS, which represent the capacity of the pool.
When the correct answer is plugged in, the time to empty the pool when the draining pipe and intake pipe work simultaneously = 6 hours.
The correct answer is likely to be divisible by the given times and rates (4 hours, 6 hours, 3 liters per hour).
Only
D is a multiple of 4, 6 and 3.
D: 36 liters
Since the draining pipe alone takes 4 hours hours to drain the pool, the draining pipe's rate = w/t = 36/4 = 9 liters per hour.
Since the draining pipe REMOVES 9 liters per hour, while the intake pipe ADDS 3 liters per hour, the net removal rate when the two pipes operate together = 9-3 = 6 liters per hour.
Since the two pipes together have a net removal rate of 6 liters per hour, the time for the two pipes together to empty the 36-liter pool = w/r = 36/6 = 6 hours.
Success!
The correct answer is
D.
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