F.6 probability X2

....Baby...

2012-10-22 6:07 am

1. A nationwide survey of seniors by the University of Michigan reveals that almost 70% disapprove of daily pot smoking according to a report in Parade. If 12 seniors are selected at random and asked their opinion. Find the probability that the no. who disappove of smoking pot daily is

(a)anywhere from 7 to 9
(b) at most 5
(c) not less than 8

2.Suppose that, on average, 1 person in 1000 makes a numerial error in preparing his or her income tax return. If 10000forms are selected at random and examined, find the probability that 6,7 or 8 of the forms contain an error.

回答 (1)

myisland8132

2012-10-22 6:36 am

✔ 最佳答案

1 Let x be the no. of seniors who disappove of smoking pot daily

P(X = x) = C(12,x) (0.7)^x (0.3)^(12 - x)

(a) P(X = 7) = 0.1585, P(X = 8) = 0.2311, P(X = 9) = 0.2397

(b) P(at most 5)

= P(X = 0) + P(X = 1) + P(X = 2) + ...+ P(X = 5)

= 0.0386

(c) P(not less than 8)

= P(X = 9) + P(X = 10) + P(X = 11) + ...+ P(X = 12)

= 0.4925

2 Let x be the no. of errors of the forms

P(X = x) = C(10000,x) (0.001)^x (0.999)^(10000 - x)

P( 6,7 or 8 of the forms contain an error)

= P(X = 6) + P(X = 7) + P(X = 8)

= 0.093 + 0.137 + 0.183

= 0.413

👍 0 👎 0