GMAT Prep - Probability

[Blast]

??

[smalishah84]

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

[logitech]

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.

[smalishah84]

Thanks logitech