Adam went into Watson's to make a purchase. He asked about pricing. "One will cost you $2, eight will cost $2, seventeen will cost $4, and six thousand will cost $8."
"All right, I’d like thirty-five," said Adam. What was he buying, and what did he pay?
Solution
Adam is buying house numbers. He evidently lives at 35 Elm Street (or some other street, but it’s 35 in any case).
If you’re doing this problem with a class, you can solicit other numbers, and you can respond with (and list) the prices. They will eventually discover that there’s a jump between nine ($2) and ten ($4), also between 99 and 100, between 999 and 1000, and so on. Pretty soon somebody will catch on that it’s about buying digits.