In: Statistics and Probability
1.
For a type of power tool, the useful life (before they break down and have to be replaced) has a population mean µ = 72 months with a population standard deviation σ = 20 months. A random sample size n = 36 is taken. What is the probability that the sample mean is less than 68 months? |
Solution :
Given that,
mean =
= 72
standard deviation =
= 20
n = 36
= 72
=
/
n = 20/
36=3.33
P(
<68 ) = P[(
-
) /
< (68-72) /3.33 ]
= P(z <-1.20 )
Using z table
= 0.1151