Last year, a random sample of 15 transaction showed a mean transaction value $45 with a standard deviation $5. This year, a random sample of 20 transactions showed a mean transaction value $55 with a standard deviation $10.

a) This is a matched-sample problem. The statistic to be used is Z

b) This is a two-sample problem. The statistic to be used is T

c) This is a matched-sample problem. The statistic to be used is T

d) This is a two-sample problem. The statistic to be used is Z