So I'm student teaching in a kindergarten classroom this semester, and we've been talking about equivalencies this week. We discussed how a quarter is the same thing as three coins put together: 2 dimes and 1 nickel.

To have the students practice equivalences, I would write on the board how many quarters (represented by a Q) and they would write in how many dimes and nickles (represented by N and D). I had originally showed them to group the coins in a triangle, but one student wrote them out in a line, and voila! DDN!