AbdurRakib wrote:

How many hours would it take Pump A and Pump B working together,each at its own constant rate,to empty a tank that was initially full?

(1) Working alone at its constant rate,Pump A would empty the full tank in 4 hours 20 minutes.

(2) Working alone,Pump B would empty the full tank at its constant rate of 72 liters per minute.

OG Q 2017 New Question(Book Question: 186)

(1) Working alone at its constant rate,Pump A would empty the full tank in 4 hours 20 minutes.

A will empty the tank in 260 minutes.

Rate of A * 260min= VOLUME TO BE EMPTIED

We don't know the rate of A or volume of the tank

INSUFFICIENT

(2) Working alone,Pump B would empty the full tank at its constant rate of 72 liters per minute.

B's rate is 72 litre per minute.

72*time = volume

We don't know volume of the tank so or how much time B takes to empty.

INSUFFICIENT

Combining 1 and 2, we still don't know the total water in the tank

rate of A*260 = 72*time of B

Even if we change rate into time or time into rate, we will still have two unknowns {volume and time} or {volume or rate}

{V and R } or {V and T}

Obvious enough we still cannot solve this equation because we do not know the volume

INSUFFICIENT

ANSWER IS E

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