The New York Times reported Laurie J FlynnSolutiona Pxbar

The New York Times reported (Laurie J. Flynn,

Solution

(a) P(xbar<0.75) = P((xbar-mean)/(s/vn) <(0.75-0.8)/(0.2/sqrt(30)))

=P(Z<-1.37 )= 0.0853

(b) P(0.7<xbar<0.9) =P((0.7-0.8)/(0.2/sqrt(30)) <Z< (0.9-0.8)/(0.2/sqrt(30)))

=P(-2.74 <Z< 2.74) =0.9939

(c) Given a=0.2, |Z(0.1)|=1.28

So xbar+/- Z*s/vn

--> 0.8+/- 1.28*(0.2/sqrt(30)

--> (0.753261,0.846739 )