# Ex 13.5, 15 - Chapter 13 Class 12 Probability

Last updated at Dec. 8, 2016 by Teachoo

Last updated at Dec. 8, 2016 by Teachoo

Transcript

Ex 13.5, 15 The probability that a student is not a swimmer is 15 . Then the probability that out of five students, four are swimmers is (A) 5C4 454 15 (B) 454 15 (C) 5C1 15 454 (D) None of these Let X : be number of swimmers Picking a student is a Bernoulli trial So, X has binomial distribution P(X = x) = nCx 𝒒𝒏−𝒙 𝒑𝒙 n = number of students = 5 Given probability that student is not a swimmer is 15 So, q = 15 ∴ p = 1 – q = 1 – 15 = 45 Hence, P(X = x) = 5Cx 𝟒𝟓𝒙 𝟏𝟓𝟓 − 𝒙 We need to find the Probability of that out of five students, four are swimmers i.e. P(X = 4) P(X = 4) = 5C4 454 155 − 4 = 5C4 𝟒𝟓𝟒 𝟏𝟓 = 5C1 𝟏𝟓 𝟒𝟓𝟒 Hence, option (A) & (C) both are correct

Chapter 13 Class 12 Probability

Serial order wise

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Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.