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From a bag containing 12 identical blue balls, y identical

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sharmin.karim
 Post subject: From a bag containing 12 identical blue balls, y identical
 Post Posted: Thu Oct 15, 2009 7:40 pm 
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Course Students


Posts: 18
From a bag containing 12 identical blue balls, y identical yellow balls, and no other balls, one ball will be removed at random. If the probability is less than 2/5 that the removed ball will be blue, what is the least number of yellow balls that must be in the bag?

A. 17
B. 18
C. 19
D. 20
E. 21
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rags99
 Post subject: Re: From a bag containing 12 identical blue balls, y identical
 Post Posted: Fri Oct 16, 2009 1:31 am 
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Students


Posts: 10
B : 18

P(blue) = 12 / (12+Y)

P(blue) < 2/5


so when you solve: 12 /12+Y = 2/5
y = 18
[editor: this is the solution to the equation, not the inequality. the first proper solution to the inequality is the first number greater than 18, which is 19.
mind the problem you're solving!]


Any other solution.
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tantrix
 Post subject: Re: From a bag containing 12 identical blue balls, y identical
 Post Posted: Fri Oct 16, 2009 10:08 pm 
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Students


Posts: 1
rags99 wrote:
B : 18

P(blue) = 12 / (12+Y)

P(blue) < 2/5


so when you solve: 12 /12+Y = 2/5
y = 18


Any other solution.


Shouldn't the answer be 19?

Since you solve for the inequality 12/(12+Y) < 2/5
you end up with y>18
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RonPurewal
 Post subject: Re: From a bag containing 12 identical blue balls, y identical
 Post Posted: Sat Oct 24, 2009 8:08 am 
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ManhattanGMAT Staff


Posts: 7146
tantrix wrote:
rags99 wrote:
B : 18

P(blue) = 12 / (12+Y)

P(blue) < 2/5


so when you solve: 12 /12+Y = 2/5
y = 18


Any other solution.


Shouldn't the answer be 19?

Since you solve for the inequality 12/(12+Y) < 2/5
you end up with y>18


correct. don't forget that you're dealing with an inequality!
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RonPurewal
 Post subject: Re: From a bag containing 12 identical blue balls, y identical
 Post Posted: Sat Oct 24, 2009 8:10 am 
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ManhattanGMAT Staff


Posts: 7146
you can also solve this problem by plugging in the answer choices.

note that 2/5 is 40%.

start with (a), since you're looking for the smallest viable solution.
(a) --> this would be 12/29, which is greater than 40%. no go.
(b) --> this would be 12/30, which is exactly 40%. no go.
(c) --> this would be 12/31, which is less than 40%. correct answer.
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