• Board contributors include instructors with "800" GMAT scores.
  • 95% of posts have replies within 24 hours.
  • Join for discounts with 800score, VeritasPrep and ManhattanGMAT


FAQ  - Register  - Search - Login 

All times are UTC - 7 hours




Post new topic Reply to topic  [ 1 post ] 
Author Message
 Post subject: GMAT Fractions
PostPosted: Wed May 08, 2013 1:47 pm 
Offline
User avatar

Joined: Fri Apr 09, 2010 2:11 pm
Posts: 454
In a tree 3/5 of the birds are robins while the rest are bluejays. If 1/4 of the robins are female and 3/4 of the bluejays are female, what fraction of the birds in the tree are male?

A. 7/15
B. 1/2
C. 11/20
D. 2/3
E. 7/10

(C) First we need to determine the fraction of the birds that are bluejays:
(fraction that are bluejays) = 1 (total birds) – 3/5 (fraction that are robins) = 5/5 (total birds) – 3/5 (fraction that are robins) = 2/5
Next, determine the fraction of all the birds that are female:
(fraction of all birds that are female) = (3/5) × (1/4) (female robins) + (2/5) × (3/4) (female bluejays) = 3/20 (female robins) + 6/20 (female bluejays) = 9/20 of all birds are female.
The fraction of male birds then is:
(fraction of all birds that are male) = 1 (total birds) – 9/20 (female birds) = 20/20 (total birds) – 9/20 (female birds) = 11/20 of all birds are male.

The alternative way:
Suppose there were 100 birds in the tree. Using the fractions in the question, you can fill up this table.

Image

Therefore 55 out of 100 birds are male, implying a fraction of
55/100 = 11/20.
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 1 post ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 2 guests


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
Template made by DEVPPL -
phpBB SEO
 
GMAT(TM) and GMAT CAT (TM) are registered trademarks of the Graduate Management Admission Council(TM). The Graduate Management Admission Council(TM) does not endorse, nor is affiliated in any way with the owner or any content of this site.