Blog

# The Quest for 700: Weekly GMAT Challenge (Answer)

Yesterday, Manhattan GMAT posted a GMAT question on our blog. Today, they have followed up with the answer:

Let t stand for the desired time, so that the drain can empty the tub in t minutes and faucet Q can fill the tub in (t – 4) minutes. Also, the drain does negative work as it empties the tub. The rates for the pipes and the drain are thus

P:

Q:

Drain:

Using the fact that all three fixtures together take 6 minutes to fill 1 tub, set up an RTW chart, and use the chart to calculate the total work quantities (shown in boldface):
 Rate (tub/min) Time (min) Work (tubs) P 1/10 × 6 = 3/5 Q 1/(t – 4) × 6 = 6/(t – 4) Drain –1/t × 6 = –6/t Total n/a n/a 1

Set up an equation:

Multiply by the common denominator, 5t(t – 4):

t = 10 OR t = –6

The negative value is absurd, so t = 10; the drain can empty the tub in 10 minutes.

A first-of-its-kind, on-demand MBA application experience that delivers a personalized curriculum for you and leverages interactive tools to guide you through the entire MBA application process.

### Upcoming Events

• Berkeley Haas (Round 1)