Question

In a manufacturing process, a machine produces bolts that have an average length of 3 inches with a variance of .03. If we randomly select three bolts from this process, what is the probability the mean length of the bolt is "at most 3.1 inches"

Answer 1

Answer: 0.8413

Step-by-step explanation:

population mean = 3

population variance = 0.03

sd (standard deviation) = √0.03

Let x = sample mean

x has a mean of 3 and sd of √0.03/√3 = √0.01 = 0.1

And we can aprox the sample mean distribution using a normal distribution

Note: this approximation maybe is not so good (n = 3)

with mean = 3 and sd = 0.1

z = (x-3)/0.1 has a standard normal distribution

P(x<3.1) = P(z<(3.1-3)/0.1) = P(z<1) =0.8413