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probability

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Manager
Manager
avatar
Status: GMAT Preperation
Joined: 04 Feb 2010
Posts: 105
Concentration: Social Entrepreneurship, Social Entrepreneurship
GPA: 3
WE: Consulting (Insurance)
Followers: 2

Kudos [?]: 24 [0], given: 15

probability [#permalink] New post 16 Oct 2010, 23:14
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
A bag contains 26 purple jellybeans, 15 green jellybeans, and 9 yellow jellybeans; these jellybeans
are the only items in the bag. If a person reaches into the bag and picks out only purple
jellybeans, how many jellybeans would the person have to pick out in order to double the
probability that a jellybean picked out of the bag at random would be a green jellybean?
A. 5
B. 15
C. 19
D. 24
E. 25
[Reveal] Spoiler: OA
Manager
Manager
avatar
Joined: 08 Oct 2010
Posts: 213
Location: Uzbekistan
Schools: Johnson, Fuqua, Simon, Mendoza
WE 3: 10
Followers: 9

Kudos [?]: 219 [0], given: 974

Re: probability [#permalink] New post 17 Oct 2010, 00:11
A bag contains 26 purple jellybeans, 15 green jellybeans, and 9 yellow jellybeans; these jellybeans are the only items in the bag. If a person reaches into the bag and picks out only purple jellybeans, how many jellybeans would the person have to pick out in order to double the probability that a jellybean picked out of the bag at random would be a green jellybean?
A. 5
B. 15
C. 19
D. 24
E. 25

The total number of jellybeans in the bag was intially 50. And the probability of picking out the green jellybeans was 15/50. But after choosing one purple jellybean the total number of jellybeans in the bag is 49. Hence, the probability of picking out the green jellybeans thereafter is 15/49.
In order to double the probability that a jellybean picked out of the bag at random would be a green jellybean the person should pick 24 more out of 49 jellybeans. Henceforth, the probability of picking out the green jellybeans will be doubled, i.e. 15/25 or 3/5 because the initial pprobability was 15/50 or 3/10.
Manager
Manager
avatar
Joined: 08 Oct 2010
Posts: 213
Location: Uzbekistan
Schools: Johnson, Fuqua, Simon, Mendoza
WE 3: 10
Followers: 9

Kudos [?]: 219 [0], given: 974

Re: probability [#permalink] New post 17 Oct 2010, 00:13
On the basis of my explanation above the answer is D
Manager
Manager
avatar
Status: GMAT Preperation
Joined: 04 Feb 2010
Posts: 105
Concentration: Social Entrepreneurship, Social Entrepreneurship
GPA: 3
WE: Consulting (Insurance)
Followers: 2

Kudos [?]: 24 [0], given: 15

Re: probability [#permalink] New post 17 Oct 2010, 01:07
To solve this problem, you would first need to figure out what it means to double the probability
of picking a green jellybean at random. Your first step would be to determine the initial odds of picking
a green jellybean; we know from the last question that those odds are 15/50 = 0.3 = 30%. Doubled
odds, therefore, are 60%, or 0.6. Since the person picking out the jellybeans in this question is picking
only purple jellybeans, we know that the number of green jellybeans remains the same, 15. If x is the
new total of jellybeans after the person picks out the purples, we can set up the equation:

0.6=15/x => x=25

So the new total of jellybeans must be 25. If the original total was 50, a person would have to pick
out 50 – 25 = 25 purple jellybeans in order to double the probability of picking a green jellybean
at random.
Manager
Manager
User avatar
Joined: 19 Aug 2010
Posts: 78
Followers: 3

Kudos [?]: 14 [0], given: 2

Re: probability [#permalink] New post 17 Oct 2010, 01:34
I also end up with 25 purple to be taken out. What is OA?
Re: probability   [#permalink] 17 Oct 2010, 01:34
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