Question

Working of a problem--I have found the mean, variance and the standard deviation from the following info:
The probability that a cellular phone company Kiosk sells X number of new phone contracts per day is shown below----
X=4, 5, 6, 8, 10
P(X)=0.4, 0.3, 0.1, 0.15, .0.05
Mean=5.4
Variance=2.94
Standard deviation=1.71

Cool with this--question--what is the probability that they will sell 6 or more contracts three days in a row??
How do I set this up?

Answer 1

Z = (score - mean)/SD = (6-5.4)/1.71 = .6/1.71 = .35

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion related to that Z score.

Since the probability that all events will occur is the product of the individual events, that proportion cubed is your answer.

Answer 2

This is familiar to me--the answer from my book is 0.027. ????