PS Topic Percentages - GMAT Tomorrow

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PS Topic Percentages - GMAT Tomorrow

by soni_pallavi » Thu Nov 22, 2012 11:03 pm
Q1)

The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present.If the concentration of chemical B is increased by 100 percent,which of the following is closest to the percentage change in the concentration of chemical A required to keep the reaction rate unchanged?

a)100% decrease
b)50% decrease
c)40% decrease
d)40% increase
e)50% increase

Ans [spoiler]D[spoiler][/spoiler][/spoiler]
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by Anurag@Gurome » Thu Nov 22, 2012 11:06 pm
soni_pallavi wrote:Q1)

The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present.If the concentration of chemical B is increased by 100 percent,which of the following is closest to the percentage change in the concentration of chemical A required to keep the reaction rate unchanged?

a)100% decrease
b)50% decrease
c)40% decrease
d)40% increase
e)50% increase

Ans [spoiler]D[spoiler][/spoiler][/spoiler]
Rate of a certain chemical reaction, R, is directly proportional A²/B
When the concentration of chemical B is increased by 100 percent, then concentration of chemical A also increases by, say, a%.
Then, R = A²/B = (aA)²/2B
A²/B = a²A²/2B
1 = a²/2
a² = 2
a = 1.4, which means there is 40% increase in the concentration of chemical A.

The correct answer is D.
Anurag Mairal, Ph.D., MBA
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