Numbers are your stock in trade, and you are, no doubt, an expert at manipulating big numbers. But do you remember the basic arithmetic of small numbers and the simple ways they relate to each other? Here’s a sequence of puzzles to test your small-number smarts. Each puzzle is designed to be solved in about 30 seconds. We start with a warmup to see how observant you are, and then the puzzles are ordered from easiest to hardest. Get your timer ready. If you can complete eight of the puzzles in a total of five minutes or less, we know you paid attention in high school.