Question: A U.S. dime is supposed to weigh 2.268 grams. A random sample of 15 circulated dimes showed a mean weight of 2.256 grams with a standard deviation of .026 grams.

(a) Using α = .05, is the mean weight of all circulated dimes lower than the specification? State your hypotheses and decision rule.

(b) Why might circulated dimes weigh less than the mint specification? (See Science

News 157, no. 14 [April 1, 2000], p. 216.)