Write on, wipe off ... and let the learning begin again Subtraction can be simple Kids can master this important area of math by completing the equations on each colorful write-on wipe-off card. Just one quick sweep of the pen's eraser and the marks are gone, so you're ready to practice again. Because the cards are color coded to indicate difficulty, kids can work their way up as they solve harder and harder problems. The pack includes 40 cards, plus...