If one has a 20% historical probability of making a sale each call during a shift where 100 calls are made..?

Question

Describe the probability distribution of x, and calculate the probability of the employee making exactly 28 sales during a 100-call shift. What is the probability that the employee will make less than 28 sales during the 100-call shift? What is the probability that the employee will make 28 or more sales during the 100-call shift?

Answer 1

P( n=k)= (1/5)^k (4/5)^(100-k) 100! / k! (100-k)! So plug in k=28, or add up the values for k>28 and k<28. You don't need to actually compute both sums since it all adds up to 1.

Answer 2

You might also use the normal distribution to approximate the binomial distribution in this problem.