Question

A compact disc is designed to last an average of 4 years with a standard deviation of 0.8 years.

What is the probability that a CD will last less than 3 years?

Answer 1

10.56%

Explanation:

Step 1: Use the z formula

The z-formula is

`z=(x-mean)/(standard | deviation)`

`z=(3-4)/(0.8) \\\\z=(-1)/(0.8) \\\\=-1.25`

P(z < -1.25)

Step 2: Use a p chart to find -1.25

-1.25 on a p chart is .1056

there is a 10.56% chance that a CD will last less than 3 years.

The answer is 10.56%

Answer 2

3-4/.8=1.25
then use the probability z chart to get
10.56%