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Sub 505 (Easy)|   Work and Rate Problems|                           
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Bunuel
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Bunuel
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Statement 1 gives the initial capacity of the tank, clearly insufficient
statement 2 gives both the rate of inflow as well as outflow which is sufficient to calculate the rate at which water is increasing per minute in the tank
Answer - B
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Got the correct answer B in 42 seconds.
No need to solve any thing in these type of Questions.
Clearly A is not sufficient and you can mark this within 20 Sec.
B gives Inflow and Outflow rate and Question is asking the Increasing Rate not the Increasing values.

People might get confused to mark C in this Question but the trick here is Question is asking for Rate of Increase not the Exact values of how much its is increased.


Hope this will help Someone..
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Statement - 1:
    We know that we have 200 gallons of water in the tank but this doesn't help us much - Clearly Insufficient
Statement - 2:
    Remember: Rates (work rates) are additive.



    In this case we have a positive work (water-in) and a negative work (water-out), however we need to ensure that before we add (or subtract) the rates, both the rates need to have the same work-time relationship.

    At this stage, we are done. We don't really need to calculate anything and we can safely say that this statement is clearly sufficient. In case you want to know the math then here goes: First we need to agree that we have an overall positive work since the rate of water-in is more than the rate of water-out.

    Tip: For work / rate problems, it is always a good trick to create a table listing down all the metrics namely worker, rate, time, and work done:
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Question is asking for the new combined rate.

Water is pumped into a partially filled tank at a constant rate through an inlet pipe. At the same time, water is pumped out of the tank at a constant rate through an outlet pipe. At what rate, in gallons per minute, is the amount of water in the tank increasing?

(1) The amount of water initially in the tank is 200 gallons.
Insufficient.

(2) Water is pumped into the tank at a rate of 10 gallons per minute and out of the tank at a rate of 10 gallons every 2 1/2 minutes.
Sufficient.

B.
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Bunuel
Water is pumped into a partially filled tank at a constant rate through an inlet pipe. At the same time, water is pumped out of the tank at a constant rate through an outlet pipe. At what rate, in gallons per minute, is the amount of water in the tank increasing?

(1) The amount of water initially in the tank is 200 gallons.
(2) Water is pumped into the tank at a rate of 10 gallons per minute and out of the tank at a rate of 10 gallons every \(2\frac{1}{2}\) minutes.





Nick Slavkovich, GMAT/GRE tutor with 20+ years of experience

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