Cryptarithms

Cool math puzzles, which I remember from my childhood (though the ones I did were in Russian). The principle is that you must solve a puzzle such as OLD+OLD+OLD = GOOD or COUPLE+COUPLE = QUARTET, where each letter stands for a digit and no two letters standing for the same digit. A fun project for kids who like math, and maybe even for adults. Thanks to my colleague Doug Lichtman for the pointer.