Question 415757
We are interested in the maximum differential between 
these spots. Data was collected for over 2300 concrete slabs. The maximum 
differential, x, had a mean of µ=0.64 inch and a standard deviation of = 0.176 inch. 
Consider a sample of n=400 slabs selected from those surveyed and let X-bar represent the 
mean of the sample. These slabs were selected without replacement from the total of 2300 
slabs collected. 

a. Find E (X-bar) = u = 0.64
----
  Var(X-bar) = [0.176/sqrt(400)]^2 = [0.0310]/400 = 0.00007744
=======================

b. Find P(X-bar >.63) 
z(0.63) = (0.63-0.64)/[0.176/sqrt(400)] = -1.1364
P(x-bar > 0.63) = P(z > -1.1364) = 0.8721
=============================
Cheers,
Stan H.
==============