GMAT PREP Probability

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poonam1279: Master | Next Rank: 500 Posts; Posts: 145; Joined: Thu Nov 13, 2008 7:18 am; Location: United Kingdom; Thanked: 5 times

by poonam1279 » Sun Dec 07, 2008 12:12 pm

Need help in solving this

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Source: Beat The GMAT — Problem Solving | Sun Dec 07, 2008 12:12 pm

earth@work: Master | Next Rank: 500 Posts; Posts: 248; Joined: Mon Aug 11, 2008 9:51 am; Thanked: 13 times

by earth@work » Sun Dec 07, 2008 4:29 pm

P(blue)=12/(12+y)<2/5
Changing to equality sign we get 12/(12+y)=2/5
y=18
now checking on number line we get ,smallest value of y=19
Ans: 19

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shafeek: Junior | Next Rank: 30 Posts; Posts: 19; Joined: Wed Dec 10, 2008 6:54 pm

by shafeek » Thu Dec 11, 2008 5:22 pm

here is something i learned about comparing fractions..
bow tie method..

n/m and x/y

which fraction is greater

cross multiply

n* y x*m

if n*y is greater then first fraction is greater otherwise the second one is greater.
this way you compare the probabilities and check which is less that 2/5
C will be the first ans..

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