Can math help come in the form of...root beer? It can now, thanks to this cool new calculator. Just fill up the three water-powered batteries with a liquid of your choice, and you’re ready for Pre-Algebra. Not only is it eco-friendly by providing “free energy”, but the science behind it is pretty neat, too: moisture activates the carbon particles and produces energy. Clear plastic over the system board allows your child to see the science taking place! (Kikkerland, $10.95)