SOLUTION: Hello, I have the following problem. Marks obtained by a number of students follows normal distribution with mean 65 and variance 25. If 3 students are taken at random, what is

Algebra ->  Probability-and-statistics -> SOLUTION: Hello, I have the following problem. Marks obtained by a number of students follows normal distribution with mean 65 and variance 25. If 3 students are taken at random, what is       Log On


   

Question 872856: Hello, I have the following problem.
Marks obtained by a number of students follows normal distribution with mean 65 and variance 25. If 3 students are taken at random, what is probability that exactly two of them will have marks over 70?
I am confused that how to find probability of " 2 out of 3 students " with given distribution of marks of students. Thanks
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!


Hi

Students: P(z >(70-65)/25) = .2 (20% score over 70)



Sample: p(over 70) = .2,   n = 3

P(x = 2) = 3C2(.2)^2(.8)^1  0r    binompdf( 3, .2, 2)= .096   0r 9.6% chance