Refer to the Statistics in Context section concerning the flower importer.
(a) Suppose it takes the importer two months to pay his invoices. Proceed by taking the sum of the adjacent one-month differences to obtain the two-month differences. Make a histogram of these differences two months apart. (The two-month differences may not be independent but the histogram is the correct summary of uncertainty for some two-month period in the future.)
(b) Compare your histogram in part (a) with that for the one-month changes. Which is more variable?