No one likes the ugly sight of a condensation ring on the coffee table. This is a problem. Thankfully, there’s a solution, and it’s full of math. These coasters will match perfectly with your number lamp and your equation bookshelf, so long as all you care about is, uh, math. The math coasters, which are available in a variety of classy colors (as pictured above), are sold in sets of five for $22.