Statistics Problem

Question

 An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed, with mean equal to 760 hours and standard deviation of 40 hours. Assume that a random sample of 16 bulbs has an average life of 780 hours.

Does this assumption prompt you to question the premise that μ=760 hours? 

Answer 1

z = (780 - 760) / (40 / √16) = 20/10 = 2.00

P(z > 2.00) = 1 - 0.9772 = 0.0228

This assumption will require you to do a one-sided or a two-sided test. There is no level of significance given, but you can assume at 5% level of significance.