Instruction 9-3 An Appliance Manufacturer Claims to Have Developed a Compact Microwave

Instruction 9-3
An appliance manufacturer claims to have developed a compact microwave oven that consumes a mean of no more than 250 W. From previous studies, it is believed that power consumption for microwave ovens is normally distributed with a population standard deviation of 15 W. A consumer group has decided to try to discover if the claim appears true. They take a sample of 20 microwave ovens and find that they consume a mean of 257.3 W.
-Referring to Instruction 9-3,for this test to be valid,it is necessary that the power consumption for microwave ovens has a normal distribution.