Probability...

[saafiin]

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]

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?

[lena]

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]

indeed. the question as originally written is invalid..