01042008, 05:21 PM


My 7th graders prefer this method, too. If they can't see an obvious relationship between the 2 denominators (x/5 and y/20) where they can just multiply the numerator, then they cross multiply. The important thing is remembering that you go from bottom and cross up. So if it were 4/7 and 5/6, you'd multiply the 7 up to the 5, then that product stays on the right. You multiply the 6 up to the 4, and it stays on the left side. With 24 on the left, and 35 on the right, you can compare the fractions.
As mathtch said, it's essentially just finding a common denominator by multiplying the numbers times each other. But it's faster for comparing 2 individual fractions than going through the steps for an LCD.
