GMAT Prep - Probability

This topic has expert replies
Senior | Next Rank: 100 Posts
Posts: 81
Joined: Fri Nov 21, 2008 7:47 am
Thanked: 2 times

GMAT Prep - Probability

by Blast » Sun Nov 23, 2008 6:10 pm
??
Attachments
1.doc
(75 KiB) Downloaded 207 times

Senior | Next Rank: 100 Posts
Posts: 73
Joined: Mon Sep 15, 2008 7:05 am
Thanked: 2 times

by smalishah84 » Sun Nov 23, 2008 11:07 pm
Man een I got this one wrongand to this day I don't know how it is to be solved. Can anybody please help.

Thanks

User avatar
Legendary Member
Posts: 2134
Joined: Mon Oct 20, 2008 11:26 pm
Thanked: 237 times
Followed by:25 members
GMAT Score:730

by logitech » Sun Nov 23, 2008 11:17 pm
Stacey from MGMAT:
25 balls
each one is red, white, or blue
each one has a number from 1 to 10

Want: white OR even (note that we DON'T want white AND even - we have to be able to strip out those that fall into both categories). To calculate, can either do:
a) probability of "white and odd" + probability of "even and not white"
b) probability of white + probability of even - probability of white & even

(1) Translated, this means there aren't any that are both white and even. This doesn't tell us how many are white or how many are even. Insufficient. Eliminate A and D.

(2) Pwhite - Peven = 0.2. So, Pwhite could be 0.4 which would make Peven 0.2. Or Pwhite could be 0.3 which would make Peven 0.1. And (by itself) it doesn't tell me Prob of even & white, which I'd need to subtract, so... insufficient in many ways. Eliminate B.

(1) AND (2) Now I know that Peven+white = 0. BUT, I still have multiple possibilities for Pwhite and Peven (see above). 0.4+0.2-0=0.6. 0.3+0.1-0=0.4. ?? Still insufficient.
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"

Senior | Next Rank: 100 Posts
Posts: 73
Joined: Mon Sep 15, 2008 7:05 am
Thanked: 2 times

by smalishah84 » Wed Nov 26, 2008 5:11 pm
Thanks logitech