Bunuel wrote:

A certain tank is filled to one quarter of its capacity with a mixture consisting of water and sodium chloride. The proportion of sodium chloride in the tank is 40% by volume and the capacity of the tank is 24 gallons. If the water evaporates from the tank at the rate of 0.5 gallons per hour, and the amount of sodium chloride stays the same, what will be the concentration of water in the mixture in 2 hours?

A. 43%

B. 50%

C. 52%

D. 54%

E. 56%

The tank of 24 gallons is filled to a quarter so it had 6 gallons of water with 40% sodium chloride. In 2 hrs, .5*2 = 1 gallon of pure water (0% sodium chloride) will evaporate.

In essence, the initial mix of 6 gallons (40% sodium chloride) was a mix of 5 gallons of x% sodium chloride and 1 gallon of pure water.

Working with sodium chloride concentrations:

w1/w2 = (A2 - Aavg)/(Aavg - A1)

5/1 = (0 - 40)/(40 - x)

x = 48

So concentration of water is 100 - 48 = 52%

_________________

Karishma

Veritas Prep GMAT Instructor

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