gmat preparation courses

It is currently Tue Jan 23, 2018 3:52 pm

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 2 posts ] 
Author Message
 Post subject: GMAT Percentage
PostPosted: Wed Jan 05, 2011 3:04 am 
Offline

Joined: Sun May 30, 2010 3:15 am
Posts: 424
John and Mike had equal amount of money in savings at the beginning of last year. Then Mike’s savings increased by 20% by the end of last year and decreased by 20% this year. John’s savings at first decreased by 20% by the end of last year and then increased by 20% this year. What percentage of John’s and Mike’s savings combined are John’s savings alone?

A. 25%
B. 40%
C. 50%
D. 75%
E. 96%

(C) Let’s denote by x amount of money each of them had in savings at the beginning of last year.

Considering changes in Mike’s savings he currently has 1.2 × 0.8 × x = 0.96x
Considering changes in John’s savings he currently has 0.8 × 1.2 × x = 0.96x

In order to calculate what percentage of John’s and Mike’s savings combined are John’s savings alone we divide Jon’s savings alone by John’s and Mike’s savings combined:
0.96x / (0.96x + 0.96 x) = 1/2 =0.5 = 50%.

The answer is C.
-----------
In this question, the assumption is that the decrease/increase in savings in the begening of this year were on the original saving amount. Why is it so?


Top
 Profile  
 
 Post subject: Re: GMAT Percentage
PostPosted: Wed Jan 05, 2011 3:19 am 
Offline

Joined: Sun May 30, 2010 2:23 am
Posts: 498
There is NO such assumption. In the explanation we apply increase/decrease simultaneously. Let's consider it in steps.

Let’s denote by x amount of money each of them had in savings at the beginning of last year.
Mike’s savings by the end of last year increased by 20%: 1.2x
John’s savings by the end of last year decreased by 20%: 0.8x

Mike’s savings decreased by 20% this year: (1.2x) × 0.8 = 0.96x
John's savings increased by 20% this year: (0.8x) × 1.2 = 0.96x

The rest of the reasoning is the same.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 2 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group