A company that manufactures light bulbs claims that its light bulbs last an aver

Question

A company that manufactures light bulbs claims that its light bulbs last an average of 1150 hours. A sample of 25 light bulbs manufactured by this company gave a mean life of 1094 hours and a standard deviation of 174 hours. A consumer group wants to test the hypothesis that the mean life of light bulbs produced by this company is less than 1150 hours. The significance level is 5%. Assume the population is normally distributed.

What is the critical value of t?

A. 1.708     

B. 1.711      

C. 2.797   

Explanation / Answer

A consumer group wants to test the hypothesis that the mean life of light bulbs produced by this company is less than 1150 hours.

Hence, this is a left tailed test.

As n = 25, then df = n - 1 = 24. Hence, at 0.05 level left tailed t test, the critical value, by table/technology is

tcrit = -1.711 [ANSWER, B]

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