The director of quality at a light-bulb factory needs to estimate the average li
ID: 3056186 • Letter: T
Question
The director of quality at a light-bulb factory needs to estimate the average life of a large shipment of light bulbs. The process standard deviation is known to be 180 hours. A random sample of 81 light bulbs indicated a sample average life of 400 hours. a Set up a 95% confidence interval (CI) estimate of the true average life of light bulbs in this shipment. a1. The critical value is a2. The lower limit of Cl is (1DP); (2DP); (1DP), and the upper limit of Cl is b. Based on your results given in part a, do you think that the manufacturer has the right to state that the light bulbs last an average of 450 hours? (enter Y for "yes", N for "No")Explanation / Answer
Ans:
a)
a-1)critical z value for 95% CI is 1.96
a-2)95% Confidence interval for true average life
=400+/-1.96*180/sqrt(81)
=400+/-1.96*20
=400+/-39.2
=(360.8, 439.2)
b)As,above CI does not include 450 within it and both limits are lower than 450,manufacturer do not have right to say that bulb's average life is 450 hrs.
No