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This series is designed to help you step up your Data Sufficiency practice while we all spend a little extra time at home during the coronavirus situation; I’m going to publish one practice Data Sufficiency question each day! You can choose to do all of them, or none of them. 

Click on the tag “Social Distancing DS Challenge” at the bottom of this post to see all of the questions in this series! 

And remember to take whatever precautions you need to stay healthy over the next few weeks! 

Question #16

Milk flows into a vat at a constant rate through a metal pipe. At the same time, milk is pumped out of the vat at a constant rate through another metal pipe. At what rate, in liters per minute, is the amount of milk in the vat decreasing?

(1) The amount of milk initially in the vat was 100 liters.

(2) Milk flows into the vat at a rate of 5 gallons every 5 minutes and out of the vat at a rate of 5 gallons per minute.

Explanation

The amount of milk initially in the vat is irrelevant, since we’re only interested in the rate of milk decrease, so statement (1) is not sufficient. Statement (2) tells us separate rates for the milk flowing into and out of the vat. Using these rates, we can find an overall rate for the decrease of milk volume.

Don’t bother finding the actual rate! To answer this question, you just need to confirm that it is possible to calculate — don’t waste time actually doing the math. Statement (2) alone is sufficient. The correct answer is (B).