Math Question plz answer?
One pump can fill a pool in 11 hours and a second pump can empty the same pool in 4 hours. While the pool is full both pumps are accidentally both turned on at the same time. How long will does it take to empty the pool?
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answers:
Como say: Let volume of pool = V units³
Rate for pump 1 = V / 11 units ³ / h
Rate for pump 2 = V / 4 units ³ / h
Net rate = V/ 4 - V/11 = ( 11V - 4V ) / 44 = 7V / 44 units ³ / h

time = V / ( 7V / 44 ) = 44 / 7 = 6 • 29 hours
time = 6 h 17 min
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sepia say: One pump can fill a pool in 11 hours and a second pump can empty the same pool in 4 hours.
While the pool is full both pumps are accidentally both turned on at the same time.
How long will does it take to empty the pool?
1 / (1/11 - 1/4) = 1 / (-7/44) = -6 2/7 hours
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khalil say: v ... volume of pool ...m³
filling pump rate = v / 11 m³/h
emptying pump rate = v / 4 m³/h
v + input - output = 0
v + [(v/11) - (v/4)] t = 0
t = 44 / 7 h
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Puzzling say: Write each value as a rate.

The first pump fills 1/11 of the pool per hour.
The second pump empties 1/4 of the pool per hour.

So the net rate is:
1/11 - 1/4
= 4/44 - 11/44
= -7/44

You start with 1 full pool and are emptying -7/44 of the pool per hour. When do you get to 0?
1 - 7/44t = 0
1 = 7/44t
t = 44/7
t = 6 2/7 hours

Answer:
6 2/7 hours (about 6 hours and 17 minutes)
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