Question

A university found that 20% of its students withdraw without completing the introductory statistics course. Assume that 20 students registered for the course. If required, round your answers to four decimal places. a. Compute the probability that 2 or fewer will withdraw. b. Compute the probability that exactly 4 will withdraw. c. Compute the probability that more than 3 will withdraw. d. Compute the expected number of withdrawals.

Answer 1

This is a binomial problem.

Let X is the random variable denoting number of  students withdraw without completing the introductory statistics course.

Given,

X ~ (20 , 0.2 )

And pmf of X is :

a. Probability that 2 or fewer will withdraw, i.e.

  

  

  

b. The probability that exactly 4 will withdraw, i.e.

  

c. The probability that more than 3 will withdraw , i.e.

   

d. The expected number of withdrawals = n*p

= 20 *0.2

= 4