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Probability

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by nikhilkatira » Sun May 16, 2010 10:28 pm
A company has 8 telephone lines. If 4 calls have to be made by the company , what is the probability that they are each made on a different line ?

(A) 35/2048
(B) 105/256
(C) 105/2048
(D) 35/256
(E) 105/128

Please answer with explanation.

Can we expect such questions in test ?
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Nikhil H. Katira
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by blackbird562 » Mon May 17, 2010 12:03 am
Ans is B. 105/256

Probability of a new line for each call is: 1 x 7/8 x 6/8 x 5/8 = 105/256
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by thephoenix » Mon May 17, 2010 3:28 am
probability= no. of favorable cases/tot # of cases
# of favorable case=8*7*6*5( first call will have 8 choices , 2nd will have 7 choices , 3rd will have 6 and 4th will have 5)
tot cases=8*8*8*8
P=8*7*6*5/8*8*8*8=105/256
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by nikhilkatira » Mon May 17, 2010 5:17 am
thank you for your valuable explanations.
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