New York's SoHo district is getting some curious out-of-home advertising lately. First, there was the Jell-O Pudding Face billboard with the live Twitter mood-ometer. Now, a mystery advertiser has put up a giant chalkboard billboard at the corner of Broome and Crosby Streets—and has begun to etch out a scary-looking math problem for you to solve. Visit the Giant Chalkboard website for a better look at the puzzle so far. According to the email we got, this is just the beginning of "an elaborate equation full of challenging twists and turns that combines mathematics with numbers that are significant to scientific human achievements throughout history." The tagline at the bottom reads: "Solutionism. The new optimism." Google once used a math problem on a billboard to recruit engineers, but we've been suspicious of math-related ads ever since that recent Farmers Insurance ad. The shadowy figures behind the chalkboard promise to reveal the rest of the puzzle, and the solution, within the next five days. And they'll apparently reveal themselves, too—it's the beginning of a Draftfcb campaign for Dow.