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

It is currently 14 Oct 2019, 04:52

Close

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
Your Progress

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.

Close

Request Expert Reply

Confirm Cancel

In a class with 12 children, q of the children are girls. Two children

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

Hide Tags

Find Similar Topics 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 58316
In a class with 12 children, q of the children are girls. Two children  [#permalink]

Show Tags

New post 28 Jan 2018, 23:40
00:00
A
B
C
D
E

Difficulty:

  75% (hard)

Question Stats:

44% (01:57) correct 56% (02:10) wrong based on 71 sessions

HideShow timer Statistics

In a class with 12 children, q of the children are girls. Two children will be randomly chosen simultaneously. What is the value of q?

(1) The probability that two girls will be chosen together is 1/11.
(2) The probability that one boy will be chosen and one girl will be chosen is 16/33.

_________________
Retired Moderator
avatar
P
Joined: 22 Aug 2013
Posts: 1431
Location: India
Re: In a class with 12 children, q of the children are girls. Two children  [#permalink]

Show Tags

New post 28 Jan 2018, 23:53
Bunuel wrote:
In a class with 12 children, q of the children are girls. Two children will be randomly chosen simultaneously. What is the value of q?

(1) The probability that two girls will be chosen together is 1/11.
(2) The probability that one boy will be chosen and one girl will be chosen is 16/33.


Out of 12 children, girls = q, Boys = (12-q).

(1) Probability of choosing two girls = q/12 * (q-1)/11 = 1/11 (Given)
Solving the above we get q*(q-1) = 12 or q=4. Thus there are 4 girls. Sufficient.

(2) Probability of choosing one boy and one girl = Probability of EITHER choosing first child as boy & second child as girl OR choosing first child as girl & second child as boy
= (12-q)/12 * q/11 + q/12 * (12-q)/11 = 16/33 (Given)
Solving the above we get: 2*q*(12-q) = 64 or q(12-q) = 32.
Here we could have either q=8 and 12-q = 4 Or we could have q=4 and 12-q = 8.
So the number of girls could be either 4 or 8, not a unique value. Not Sufficient.

Hence A answer
CEO
CEO
User avatar
D
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 2974
Location: India
GMAT: INSIGHT
Schools: Darden '21
WE: Education (Education)
Reviews Badge
In a class with 12 children, q of the children are girls. Two children  [#permalink]

Show Tags

New post 29 Jan 2018, 07:12
Bunuel wrote:
In a class with 12 children, q of the children are girls. Two children will be randomly chosen simultaneously. What is the value of q?

(1) The probability that two girls will be chosen together is 1/11.
(2) The probability that one boy will be chosen and one girl will be chosen is 16/33.


ATTENTION!!! : Since this is a Data Sufficiency question therefore it's important for us to understand that we need not get into the entire calculation to find the value of q. Instead all we need to know is whether the information given is sufficient to answer the question or not.

Question : Number of girls, q = ?

Statement 1: The probability that two girls will be chosen together is 1/11.

i.e. qC2 / 12C2 = 1/11 . Unique solution to follow as q is positive, hence
SUFFICIENT

Statement 2:The probability that one boy will be chosen and one girl will be chosen is 16/33.

i.e. qC1 * (12-q)C1 / 12C2 = 16/33 . But here the value of q and (12-q) will be interchangeable and might be different if q≠6 so we need to calculate the exact value of q,

i.e. q = 8 or 4 hence
NOT SUFFICIENT

Answer: Option A
_________________
Prosper!!!
GMATinsight
Bhoopendra Singh and Dr.Sushma Jha
e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772
Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi
http://www.GMATinsight.com/testimonials.html

ACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION
GMAT Club Bot
In a class with 12 children, q of the children are girls. Two children   [#permalink] 29 Jan 2018, 07:12
Display posts from previous: Sort by

In a class with 12 children, q of the children are girls. Two children

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





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