Question

A manufacturer claims his light bulbs have a mean life of 1800 hours. A consumer group wants to test if their light bulbs do not last as long as the manufacturer claims. They tested a random sample of 270 bulbs and found them to have a sample mean life of 1790 hours and a sample standard deviation of 60 hours. Assess the manufacturer's claim. a) What is the null hypothesis? Correct: y = 1800 Incorrect x = 1800 Incorrect x < 1800 Incorrect u > 1800 You are correct. Previous Tries Your receipt no. is 153-3579 b) What is the alternative hypothesis? Incorrect p > 1800 Incorrect i < 1800 Incorrect x > 1800 Correct: u < 1800 You are correct. Previous Tries Your receipt no. is 153-2216 c) Give the value of the test statistic, to two places past the decimal point. Submit Answer Incorrect. Tries 2/5 Previous Tries

Answer 1

c)

Standard Error , SE = s/√n =   60.0000   / √    270   =   3.6515      
t-test statistic= (x̅ - µ )/SE = (   1790.000   -   1800   ) /    3.6515   =   -2.74 (answer)