CBSE Class 12-science Answered
Probability
Asked by | 23 Mar, 2010, 01:48: AM
Expert Answer
(d) None of these.
The probabilities are binomial distribution.
Probability of getting 7 heads,
P(7) = n!(0.5)7(0.5)n-7/(7!(n-7)!) = n!(0.5)n/(7!(n-7)!)
Similarly, probability of getting 9 heads,
P(9) = n!(0.5)9(0.5)n-9/(9!(n-9)!) = n!(0.5)n/(9!(n-9)!)
We require, P(7) = P(9)
Hence we get
(9!(n-9)!) = (7!(n-7)!)
(n-7)! = (n-9)!x(n-8)x(n-7)
8x9 = (n-8)x(n-7) = n2 - 15n + 56
n2 - 15n + 56 = 72
n2 - 15n - 16 = 0
(n-16)(n+1) = 0
n = 16.
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Team,
TopperLearning.
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