Question

The tensile strength of paper is modeled by a normal distribution with a mean of 35 pounds per square inch and a standard deviation of 2 pounds per square inch. what is the probability that the strength of a sample is less than 38 lb/in2? round your answer to 4 decimal places.

Answer 1

Given
mean=35 psi
std dev=2 psi
distribution normal

For probability that X<38, 
calculate
Z score = (X-mean)/std dev
=(38-35)/2=1.5
P(X<38)
=P(Z<1.5)
=0.9331928  from tables.

So probability that the strength of a random sample <38 pis = 0.9332