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Solution to Figure 7.5 Most people try to correct the equations in Figure 7.5 by moving a matchstick that changes one of the numbers. Why? Because solving the math problems that we are assigned in school almost always involves manipulating the numbers, not the arithmetic signs. While this assumption is a useful one in solving the vast majority of math problems—especially the ones that you are assigned as homework—it is an example of a mental set that can block you from arriving at new, creative solutions to problems.