Question

In: Statistics and Probability

1. For a type of power tool, the useful life (before they break down and have...

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?

Solutions

Expert Solution

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   

orchestra answered 2 years ago
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