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Wed Mar 25, 2020 1:39 am

GMAT Prep

Chlorination is used in industry for the purification of water; 1 g solution of chlorine will remove half of the germs in 1 liter of water. If the water containing less than 0.09% is considered clean, what is the minimum amount of chlorine required to purify 150 liters of water containing 0.3 liters of harmful substances?

A. 1
B. 2
C. 3
D. 4
E. 5

OA B

The water has 0.3 liters of harmful substances and needs to be reduced to less than 0.0009 x 150 = 0.135 liters in order to be considered clean. If we add 1 gram of chlorine to the solution, half of the germs will be removed and we will be left with 0.3 x 1/2 = 0.15 liters of harmful substances. If we add another gram of chlorine, there will be 0.15 x 1/2 = 0.075 liters of harmful substances remaining in the water, which is a low enough figure for the water to be considered clean. Thus, we need 2 grams of chlorine in total.

Answer: B