The problem seems to be limited to pennies, nickels, dimes and quarters; if so there are two solutions (and if not I think the problem is even more poorly framed, if possible). The kids given this problem aren't learning combinatorics, really, but doing the same old EM stuff about adding up whole numbers in different ways, because at that level EM's obsession is building up number sense by combining numbers in different ways. I'd be thrilled if this problem had been presented correctly in the context of learning some combinatorics.
Besides the limiting constraint of exactly four quarters, Stella has to have exactly five coins, Joan has to have exactly ten coins, and Joan has to have double Stella's amount of money. It's neat that you're able to model the problem at all in a spreadsheet-- I'm pretty happy when I can get things to total up correctly in Excel, and never delved into programming it.
