I just went through the GMATPrep exam, and there were 2 DS questions which I had no idea how to go about it. Can someone help me out?
Thanks in advance!
GMAT Prep ques:
This topic has expert replies
-
- Senior | Next Rank: 100 Posts
- Posts: 60
- Joined: Fri Jun 01, 2007 11:02 pm
- jayhawk2001
- Community Manager
- Posts: 789
- Joined: Sun Jan 28, 2007 3:51 pm
- Location: Silicon valley, California
- Thanked: 30 times
- Followed by:1 members
Problem 1:
P(white or even) = P(white) + P(even) - P(white & even)
1 - insufficient. We don't know P(white) and P(even)
2 - insufficient. We don't know P(white & even)
1 & 2 insufficient. We just know P(white) - P(even). We can't find out
P(white) + P(even)
--------------------------------------------------------------------------------------
Problem 2:
1 - insufficient. Take x=30, y=50 and x=70,y=50. We can get
multiple values for xy. No unique soln.
2 - insufficient. LCM=180. Can be x=45, y=4 or x=9,y=20. No
unique value
1 & 2 together sufficient.
180 = 10 * 2 * 3 * 3
We know 10 has to be a factor of both numbers. We also know that 3
cannot be a factor of both numbers (else the greatest common factor
will be 90, not 10).
So, only possible way to split this is 10*2, 10*3*3 i.e. 20,90 or 90,20
both of which yield the same value for xy.
P(white or even) = P(white) + P(even) - P(white & even)
1 - insufficient. We don't know P(white) and P(even)
2 - insufficient. We don't know P(white & even)
1 & 2 insufficient. We just know P(white) - P(even). We can't find out
P(white) + P(even)
--------------------------------------------------------------------------------------
Problem 2:
1 - insufficient. Take x=30, y=50 and x=70,y=50. We can get
multiple values for xy. No unique soln.
2 - insufficient. LCM=180. Can be x=45, y=4 or x=9,y=20. No
unique value
1 & 2 together sufficient.
180 = 10 * 2 * 3 * 3
We know 10 has to be a factor of both numbers. We also know that 3
cannot be a factor of both numbers (else the greatest common factor
will be 90, not 10).
So, only possible way to split this is 10*2, 10*3*3 i.e. 20,90 or 90,20
both of which yield the same value for xy.