GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 15 Oct 2019, 05:40 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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  M15-09

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

Hide Tags

Math Expert V
Joined: 02 Sep 2009
Posts: 58333

Show Tags 00:00

Difficulty:   5% (low)

Question Stats: 92% (01:19) correct 8% (01:51) wrong based on 48 sessions

HideShow timer Statistics

If the value of fraction $$\frac{A}{B}$$ ($$A \lt B$$) will not change if $$A$$ grows by 6 and $$B$$ grows by 15, which of the following is equal to $$\frac{B}{A}$$?

A. 2.0
B. 2.1
C. 2.5
D. 2.8
E. 3.0

_________________
Math Expert V
Joined: 02 Sep 2009
Posts: 58333

Show Tags

1
Official Solution:

If the value of fraction $$\frac{A}{B}$$ ($$A \lt B$$) will not change if $$A$$ grows by 6 and $$B$$ grows by 15, which of the following is equal to $$\frac{B}{A}$$?

A. 2.0
B. 2.1
C. 2.5
D. 2.8
E. 3.0

$$\frac{A}{B} = \frac{A + 6}{B + 15}$$. From here $$B(A + 6) = A(B + 15)$$ or $$6B = 15A$$ or $$\frac{B}{A} = \frac{15}{6} = 2.5$$.

_________________
Senior Manager  S
Joined: 08 Jun 2015
Posts: 420
Location: India
GMAT 1: 640 Q48 V29 GMAT 2: 700 Q48 V38 GPA: 3.33

Show Tags

Given that A/B=(A+6)/(B+15), cross multiply to get the ratio between B and A. The answer comes out to be 2.5 i.e. option C
_________________
" The few , the fearless "
Manager  B
Joined: 30 Apr 2013
Posts: 76

Show Tags

Can we back solve this question anyway?
Manager  S
Joined: 28 Jun 2018
Posts: 130
Location: Bouvet Island
GMAT 1: 490 Q39 V18 GMAT 2: 640 Q47 V30 GMAT 3: 670 Q50 V31 GMAT 4: 700 Q49 V36 GPA: 4

Show Tags

santro789 wrote:
Can we back solve this question anyway?

Hey santro789

Sure u can! But it is just too time consuming.

When back solving always remember to start from the middle option so that you know wether u should test higher values or lower values.
Luckily in this question 2.5 is the middle value and we can arrive at the AC quick.
So since it is a fraction it wont matter if u take A/B as 2/5 or 200/500. Just make sure B/A is equal to 2.5 because we are testing for it.
You will see that by adding the A and B with 6 and 15 will always give us $$\frac{2}{5}$$.
Example - $$\frac{2}{5}$$ is $$\frac{2+6}{5 +15}$$ = $$\frac{8}{20}$$ = $$\frac{2}{5}$$.
Hence C is the option.

Hope it helps!
Intern  B
Joined: 02 Feb 2018
Posts: 31

Show Tags

Bunuel How can we get from 6B=15A to B/A=15/6 without knowing that A is not 0? Thanks!
Intern  B
Joined: 15 Dec 2018
Posts: 6

Show Tags

Hi Bunuel,

Is the below approach correct.

As mentioned in the question the ratio will not change if 6 is added to A and 15 is added to B.
Thus 6/15 will have the same ratio as A/B.
So to find B/A => just do 15/6 =2.5

Thanks Re: M15-09   [#permalink] 15 Jun 2019, 23:26
Display posts from previous: Sort by

M15-09

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

Moderators: chetan2u, Bunuel

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne  