Bob has a bulb factory that produces white light bulbs. He sold some bulbs to Peter claiming that on average the service life of his bulbs is at least 980 hours. To test this claim Peter gathered information on the 20 bulbs purchased. He found that the mean service life is 960 and knows that the variance of service life for the population is . Which of the following statements properly analyzes Bob’s claim? Assume that the distribution service life of bulbs is normal. a. Using a t-test you conclude that both types of bulbs have different mean service life at the 5% level.
b. Using a t-test you conclude that both types of bulbs have the same mean service life at the 5% level.
c. Using a z-test you conclude that both types of bulbs have the same mean service life at the 5% level.
d. Using a t-test you conclude that both types of bulbs have the same mean service life at the 1% level.
e. Using a z-test you conclude that both types of bulbs have different mean service life at the 5% level.