Question

Required information In a sample of 80 light bulbs, the mean lifetime was 1217 hours with a standard deviation of 51 hours. Someone says that the mean lifetime is less than 1220 hours. With what level of confidence can this statement be made? (Express the final answer as a percent and round to two decimal places.) The level of confidence is 0 %.

Answer 1

70.06

Explanation:

Given the mean = 1217

Standard deviation = 51

And sample size = 80

Mean of bar x = 1217

Sd/√n

= 51/√80

= 5.7060

P(bar x<1220)

P(z < 1220-1217/5.7020)

= P(z<0.5261)

= 0.7006

Therefore the level of confidence in response to this question is 0.7006.

This statement can be made with 70.06% level of confidence.