Ostensibly, all three of these problems are accessible to high school students. None of themrequire mathematical knowledge beyond algebra, and all of them have straightforward solutions.Yet college students and professional mathematicians attack these problems in dramaticallydifferent ways.On Problem I most students will laboriously multiply the four factors on the left, subtract theterms on the right, and then try to prove that ( ab + ac +ad+ be+ bd + cd- abc- abd- acd- bed+abed)> 0-usually without success. Virtually all of the mathematicians I've watched solving itbegin by proving the inequality (I- a)(l- b)> I-a- b. Then they multiply this inequality, intum, by (I- c) and (I- d) to prove the three- and four-variable versions of it.Likewise in Problem 2, most students begin by doing the addition and placing all the termsover a common denominator. A typical expert, on the other hand, begins with the observation:"That looks messy. Let me calculate a few cases." The inductive pattern is clear and easy toprove.