Suppose a random sample of online grocery prices (15 items) is obtained at Amazon and Walmart. The same items were sampled at both sites, and a student wants to determine whether the typical price differs at the two online sites. Which test(s) can be used for each situation below?

a. Suppose the distribution of prices at each site is strongly right-skewed and the distribution of differences in prices is also strongly right-skewed.

b. Suppose the distribution of prices at each site is right-skewed but the distributions of the differences in prices is approximately Normal.

c. Suppose the sample size was 150 rather than 15 and the distribution of differences is skewed.

Choose from the following tests, as appropriate: paired t-test, sign test, two-sample t test, and Mann-Whitney test. There may be two acceptable choices.