BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

GMAT PREP I PERCENT

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 266
Joined: Mon Oct 19, 2009 9:46 pm
Thanked: 8 times
GMAT Score:690

GMAT PREP I PERCENT

by pkw209 » Tue Dec 29, 2009 10:21 am
Hey all,

Couldn't figure this one out. A brief explanation would be very much appreciated. Thanks!

The rate of a reaction is directly proportional to the square of the concentration of A and inversely proportional to concentration of B. If B increases by 100%, which of the following is closest to the % change in concentration of A required to keep the rate unchanged?

a. 100% decrease
b. 50% decrease
c. 40% decrease
d. 40% increase
e. 50% increase
Top
Source: — Problem Solving |
Junior | Next Rank: 30 Posts
Posts: 11
Joined: Fri Dec 11, 2009 10:15 am
Thanked: 2 times

by anu009 » Tue Dec 29, 2009 11:24 am
is it d 40% increase
what is the answer
Top
Senior | Next Rank: 100 Posts
Posts: 98
Joined: Mon Nov 23, 2009 2:30 pm
Thanked: 26 times
Followed by:1 members

by ace_gre » Tue Dec 29, 2009 11:32 am
Rate R = K * A^2 / B.
B==>2B( increase 100%), then R = K * A^2/ (2*B).

In order for R to be same, A==>√2 A==>1.414 A.
Hence ~ 41% increase in A will keep R the same.

I agree with anu009. Answer is D
Top
Master | Next Rank: 500 Posts
Posts: 266
Joined: Mon Oct 19, 2009 9:46 pm
Thanked: 8 times
GMAT Score:690

by pkw209 » Wed Dec 30, 2009 12:28 pm
thanks guys, you're both correct. answer is d

ace-can you please explain why you need to take the sqrt of 2A? i understand 2A but why the sqrt? I was able to figure this out by plugging in numbers but want to understand algebraically. thanks.
Top
Post new topic Post Reply
• Page 1 of 1