| Author |
Message |
|
saafiin
|
Post subject: Probability... Posted: Mon Nov 21, 2011 9:05 pm |
|
 |
| Forum Guests |
|
|
Posts: 7
|
|
Q: In a certain bag there are 12 identical blue balls, y identical yellow balls and no other ball. One ball will randomly removed. If the probability is less than 2/3 that the removed ball will be blue, then what is the least number of yellow balls that must be in the bag?
a. 17 b. 18 c. 19 d. 20 e. 21
please need help...unable to solve...
|
|
 |
|
 |
|
tim
|
Post subject: Re: Probability... Posted: Wed Nov 23, 2011 2:16 pm |
|
 |
| ManhattanGMAT Staff |
|
|
Posts: 2242 Location: Southwest Airlines, seat 21C
|
|
How far did you get on this question, and what part(s) of the solution didn’t make sense to you? For that matter, where did this problem come from?
_________________ Tim Sanders Manhattan GMAT Instructor
|
|
 |
|
 |
|
lena
|
Post subject: Re: Probability... Posted: Sat Jan 28, 2012 11:56 pm |
|
 |
| Students |
|
|
Posts: 4
|
|
I think the probability in your question is wrong. If the probability is less than 2/3 that the removed ball is blue, then the ratio of yellow balls to the total # of balls should be greater than 1/3. From here: y/(12+y)>1/3 y>6 so y=7 would be the least possible number of yellow balls
so either I have it wrong or your probability is wrong....
|
|
 |
|
 |
|
tim
|
Post subject: Re: Probability... Posted: Thu Feb 02, 2012 7:22 pm |
|
 |
| ManhattanGMAT Staff |
|
|
Posts: 2242 Location: Southwest Airlines, seat 21C
|
|
indeed. the question as originally written is invalid..
_________________ Tim Sanders Manhattan GMAT Instructor
|
|
 |
|
 |
|