Solve Problem 2 with the extra assumption that the investments can be grouped naturally as follows: 1–4, 5–8, 9–12, 13–16, and 17–20.

a. Find the optimal investments when at most one investment from each group can be selected.

b. Find the optimal investments when at least one investment from each group must be selected. (If the budget isn’t large enough to permit this, increase the budget to a larger value.)