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a dreamy vacation

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a dreamy vacation

by sanju09 » Tue May 24, 2011 1:25 am
In a department store prize box, 40% of the notes give the winner a dreamy vacation; the other notes are blank. What is the approximate probability that 3 out of 5 people that draw the notes one after the other, and immediately return their note into the box get a dreamy vacation?
(A) 0.12
(B) 0.23
(C) 0.35
(D) 0.45
(E) 0.65


[spoiler]Source: Eric's collection on BTG


OA B[/spoiler]
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by manpsingh87 » Tue May 24, 2011 1:39 am
sanju09 wrote:In a department store prize box, 40% of the notes give the winner a dreamy vacation; the other notes are blank. What is the approximate probability that 3 out of 5 people that draw the notes one after the other, and immediately return their note into the box get a dreamy vacation?
(A) 0.12
(B) 0.23
(C) 0.35
(D) 0.45
(E) 0.65


[spoiler]Source: Eric's collection on BTG


OA B[/spoiler]
out of 5 people 3 winners can be selected in 5C3 ways and their winning probability will be 0.4( it won't change because notes are returned into the box after every turn); and the remaining 2 will be the losers ( probability of losing= 1- winning= 1-.4=0.6) whose losing probability will be 0.6 each,
hence required probability is 5C3*0.4*0.4*0.4*0.6*0.6= 10*.064*.36=.2304 hence B
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