Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 30 Aug 2016, 02:18

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# m12#05 - DS

Author Message
Director
Joined: 25 Aug 2007
Posts: 954
WE 1: 3.5 yrs IT
WE 2: 2.5 yrs Retail chain
Followers: 74

Kudos [?]: 1160 [0], given: 40

### Show Tags

12 Jun 2010, 05:40
If $$a,b,c,d$$ are positive numbers, is $$\frac{a}{b}<\frac{(a+c)}{(b+d)}$$?

1. $$\frac{a}{b}<\frac{c}{d}$$
2. $$a+c<b+d$$

The OA is A, but, I have one doubt:
From S1, we can say $$\frac{a}{c}<\frac{b}{d}$$

On adding 1 on both sides, the equation becomes:
$$\frac{(a+c)}{c}<\frac{(b+d)}{d}$$
$$\frac{(a+c)}{(b+d)}<\frac{c}{d}$$

But, we are given $$\frac{a}{b}<\frac{c}{d}$$

So, S1 is insufficient. Please explain where I am missing the point.
_________________

Tricky Quant problems: http://gmatclub.com/forum/50-tricky-questions-92834.html
Important Grammer Fundamentals: http://gmatclub.com/forum/key-fundamentals-of-grammer-our-crucial-learnings-on-sc-93659.html

Math Expert
Joined: 02 Sep 2009
Posts: 34496
Followers: 6297

Kudos [?]: 79906 [0], given: 10022

### Show Tags

12 Jun 2010, 08:47
ykaiim wrote:
If $$a,b,c,d$$ are positive numbers, is $$\frac{a}{b}<\frac{(a+c)}{(b+d)}$$?

1. $$\frac{a}{b}<\frac{c}{d}$$
2. $$a+c<b+d$$

The OA is A, but, I have one doubt:
From S1, we can say $$\frac{a}{c}<\frac{b}{d}$$

On adding 1 on both sides, the equation becomes:
$$\frac{(a+c)}{c}<\frac{(b+d)}{d}$$
$$\frac{(a+c)}{(b+d)}<\frac{c}{d}$$

But, we are given $$\frac{a}{b}<\frac{c}{d}$$

So, S1 is insufficient. Please explain where I am missing the point.

Given: $$a$$, $$b$$, $$c$$, and $$d$$ are positive numbers. Question: is $$\frac{a}{b}<\frac{(a+c)}{(b+d)}$$? --> as all numbers are positive we can safely crossmultiply --> is $$ab+ad<ab+bc$$? --> is $$ad<bc$$? is $$\frac{a}{b}<\frac{c}{d}$$?

(1) Directly gives the answer. Sufficient.
(2) Not sufficient.

We can get the answer the way you were doing too: $$\frac{a}{b}<\frac{c}{d}$$ --> $$\frac{d}{b}<\frac{c}{a}$$ --> add 1 to both sides --> $$\frac{d}{b}+1<\frac{c}{a}+1$$ --> $$\frac{d+b}{b}<\frac{c+a}{a}$$ --> $$\frac{a}{b}<\frac{a+c}{b+d}$$.

Hope it helps.
_________________
Director
Joined: 25 Aug 2007
Posts: 954
WE 1: 3.5 yrs IT
WE 2: 2.5 yrs Retail chain
Followers: 74

Kudos [?]: 1160 [0], given: 40

### Show Tags

12 Jun 2010, 08:56
Bunuel,

Thanks for the explainations. But, I am still not clear where in my explaination I am missing. Can you please check?
_________________

Tricky Quant problems: http://gmatclub.com/forum/50-tricky-questions-92834.html
Important Grammer Fundamentals: http://gmatclub.com/forum/key-fundamentals-of-grammer-our-crucial-learnings-on-sc-93659.html

Math Expert
Joined: 02 Sep 2009
Posts: 34496
Followers: 6297

Kudos [?]: 79906 [0], given: 10022

### Show Tags

12 Jun 2010, 09:21
ykaiim wrote:
Bunuel,

Thanks for the explainations. But, I am still not clear where in my explaination I am missing. Can you please check?

You are not missing anything.

If we are given that $$a$$, $$b$$, $$c$$, and $$d$$ are positive numbers and $$\frac{a}{b}<\frac{c}{d}$$, then $$\frac{(a+c)}{(b+d)}<\frac{c}{d}$$ (the inequality you derived) is true. We are just asked to derive another inequality (the one I derived) not this one.
_________________
Re: m12#05 - DS   [#permalink] 12 Jun 2010, 09:21
Similar topics Replies Last post
Similar
Topics:
DS question 0 14 Dec 2011, 05:07
DS q 1 06 Jun 2011, 23:55
DS problem 1 19 Jan 2010, 19:01
DS:m 15 #29 1 20 Jun 2009, 11:59
6 M04 DS # 11 6 13 Dec 2008, 18:40
Display posts from previous: Sort by

# m12#05 - DS

Moderator: Bunuel

 Powered by phpBB © phpBB Group and phpBB SEO Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.