Question

. A normal population has mean μ = 35 and standard deviation σ = 8.

a. What proportion of the population is between 20 and 30?

b. A normal population has mean μ = 35 and standard deviation σ = 8.

Answer 1

Solution :

Given that ,

mean = = 35

standard deviation = = 8

P(20< x <30 ) = P[(20 -35) / 8< (x - ) / < (30 -35) / 8)]

= P( -1.875< Z <-0.625 )

= P(Z < -0.625) - P(Z <-1.875 )

Using z table   

= 0.266-0.0304

=0.2356

   answer=0.2356