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probability

by rahul.s » Sat Jan 30, 2010 7:06 am
A store buys 10 loaves of bread, including 7 baguettes. If that day, it sells 6 loaves of bread one by one, what is the probability of the store selling exactly 4 baguettes among the 6 loaves sold? (Assume that every loaf has an equal chance of selling)

A) 2/5
B) 3/5
C) 2/3
D) 1/2
E) 4/7

OA: D
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by thephoenix » Sat Jan 30, 2010 7:14 am
tot no. of ways for selling 6 out of 7=10c6

out of 7 bag 4 can be sold in 7c4

2 loaves out of 3 can be sold in 3c2

prob=7c4*3c2/10c6=1/2
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by ajith » Sat Jan 30, 2010 12:33 pm
rahul.s wrote:A store buys 10 loaves of bread, including 7 baguettes. If that day, it sells 6 loaves of bread one by one, what is the probability of the store selling exactly 4 baguettes among the 6 loaves sold? (Assume that every loaf has an equal chance of selling)

A) 2/5
B) 3/5
C) 2/3
D) 1/2
E) 4/7

OA: D
Number of ways of selecting 6 out of 10 = 10C6 = 10*9*8*7/24 = 210
Ways of selecting 4 baguettes among 7 = 7C3 = 35
Ways of selecting 2 out of 3 loaves = 3C2 = 3

Probability = 7c3*3c2/210 =1/2
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