Hey mathhelpforum! I'm stuck on a rather simple exercise from Applied statistics and probabilities for engineers, 4th edi.

it is exercise 7.9. the solution is supposed to be 0,2312.

I try to use the formula Z = (Sample mean - mean) / ((standard deviation)*n^(1/2)),

so for the first limit, X>2.1, I get (2.1 - 2)/((1/108)^(1/2)). It gives a Z-value of 1.04.

with sample mean 2.5, the Z-value is waaaaaaay to high.

What is wrong here? Where is everything falling apart?

Also, first post, so please correct me if there's something off about the presentation of the question.