Poor arithmetic skills often lead shoppers to make bad choices, researchers at the University of Miami say. Researchers from the university\'s school of business tracked 600 consumers during the two-year study, the South Florida Sun-Sentinel reported. Michael Tsiros, a marketing professor who led the project, said shoppers tend to believe that a choice that gives them more of a product, like a two-for-one deal or a large economy size, is automatically the best one. \"Even though the promotions may be economically equivalent, more people were taking advantage of the bonus packs,\" Tsiros said. One group was given a choice between loose coffee beans at a 33 percent discount and 33 percent more beans for the same price. Most went for the second option even though the first is a better deal.