Question: For each situation, state the null and alternative hypothesis.

a) Researchers have postulated that, due to differences in diet, Japanese children have a lower mean blood cholesterol level than U.S. children. Suppose that the mean level of U.S. children is known to be 170.

b) A water quality control board reports that water is unsafe for drinking if the mean nitrate concentration exceeds 30 ppm. Water specimens are taken from a well.

c) Last year, your company ‘s service technicians took an average of 2.6 hours to respond to trouble calls from business customers who had purchased service contracts. Do this year’s data show a different average response time?

d) Census Bureau data show that the mean household income in the area served by a shopping mall is $42,500 per year. A market research firm questions shopper at the mall. The researchers suspect that mean household income of mall shoppers is higher than that of the general population.

e) The diameter of a spindle in a small motor is supposed to be 5 mm. If the spindle is either too small or too large, the motor will not work properly. The manufacturer measures the diameter in a sample of the motors to determine whether the mean diameter has moved away from the target.