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probability/combinations problem

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probability/combinations problem

by rtaha2412 » Sat Dec 25, 2010 11:28 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
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by anshumishra » Sat Dec 25, 2010 11:54 am
rtaha2412 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
total 10 loaves
7 - baguettes
3 - non-baguettes


Out of the 6 loaves sold, we want to calculate the probability that exactly 4 among theses 6 loaves were baguettes.

So probability (4 baguettes and 2 non-baguettes were sold) = (7C4)*(3C2)/(10C6) = 1/2.

Answer is D.
Thanks
Anshu

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by diebeatsthegmat » Sat Dec 25, 2010 5:50 pm
rtaha2412 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
did the same as anshumishra
and found the answer also D
take 4 out of 7 : 7!/3!4!
take 2 out of 3 left 3!/2!
total = 35*3/210 =1/2
210=10!/6!4!
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