Teacher, "Why do we CROSS MULTIPLY?"Students, "Because it is COOL!"My father, Mick Constuble had a credential called, "Life", which meant that he could teach anything -- Advanced French 4, English Composition or even Advanced Placement Calculus. When I became a teacher in 1985, I will never forget him telling me, "The single most important mathematics concept that I taught was CROSS MULTIPLYING." That stuck with me. I hadn't realized how frequently that I would cross multiply in my mathematics j