Question

The mean annual rainfall in a particular region is 80 inches with a standard deviation of 8 inches. If a sample of 32 years is selected, what is the probability that the mean annual rainfall for this sample will be less than 79 inches?

Answer 1

Solution :

Given that ,

mean =   = 80

standard deviation = = 8

n = 32

= 80

=  / n = 8/ 32 =1.4142

P( < 79 ) = P[( - ) / < (79 -80) / 1.4142]

= P(z <-0.71 )

Using z table  

= 0.2389   

probability= 0.2389