Please provide an explanation The average life of light bulb

Please provide an explanation.

The average life of light bulbs produced by SABA Electric Co. is believed to be normally distributed with the mean service life of 920 hours and a standard deviation of 100 hours. A random sample of 100 bulbs is tested and it has a mean life of 905 hours. Can it be concluded that the mean service life of the bulbs is less than the expectation at 1% level of significance?

A. Yes. The mean service life of the bulbs is less than the expectation.

B. No. The mean service life of the bulbs is not less than the expectation.

C. No. The mean service life of the bulbs is more than the expectation.

D. None of the above.

Do employees perform better at work with music playing? Music was turned on during the working hours of a business with 49 employees and their productivity level averaged 5.2. A national study shows that when music is off employees\' productivity level is 4.8 on average, with a population standard deviation of 2.1. What can we conclude at the 1% level of significance?

A. Yes. Employees perform better at work with music playing.

B. No. Employees don’t perform better at work with music playing.

C. Employees productivity drops at work with music playing.

D. None of the above

Solution

1) EXPECTATION WAS 920

AND IN THE LOT THERE WAS 100 BULBS WITH MEAN OF 905 EXPECTATION OF SIGNIFICANCE WAS 1%

1% OF 920 IS 9.2

920-9.2 = 910.8

SO THE ANSWER WILL YES MEAN SERVICE OF BULB IS LESS THAN EXPECTATION

HENCE OPTION A