ACT probability question

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Night reader: Legendary Member; Posts: 1337; Joined: Sat Dec 27, 2008 6:29 pmFollowed by: 10 members; Thanked: 127 times

by Night reader » Mon Dec 20, 2010 1:44 pm

A box contains 7 blue marbles, 4 red marbles and 6 green marbles. How many additional blue marbles must be added in the box so that the probability of randomly drawing a blue marble is 1/2?

A. 2
B. 3
C. 4
D. 5
E. 6

ACT questions might be well GMAT questions

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Source: Beat The GMAT — Problem Solving | Mon Dec 20, 2010 1:44 pm

anshumishra: Legendary Member; Posts: 543; Joined: Tue Jun 15, 2010 7:01 pmFollowed by: 3 members; Thanked: 147 times

by anshumishra » Mon Dec 20, 2010 2:41 pm

Lets suppose, we need to add "x" blue balls,

So, (7+x)/(17+x) = 1/2
=> x =3.

Thanks

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