Learning Target

Add and subtract with fractions with unlike denominators and justify your solutions using manipulatives and mathematical reasoning.

Sample Problem

 6/7+5/8=x

6/7 - 48/56

5/8 - 35/56         48+35=83 ------ 83/56 ------ 1 27/56

Lesson

To add two fractions with unlike denominators together, you must find the Least Common Denominator (L.C.D.) by finding the smallest number that both denominators are divisable by. Then, take the number that you multiply by to get the L.C.D. and multiply it by the numerator of each fration. Those numbers are the numerators of the new fractions. Then, find the sum of the numerators and put them over the same denominator. If it is an improper fraction, subtract the denominator from the numerator and use that number as your numerator, while the denominator remains the same. Add a one to that fraction and then simplify.

To subtract two fractions with unlike denominators from each other, you must follow the same algorithm as when you add fractions with unlike denominators, but you must subtract the numerators instead of adding them. Then simplify the fraction.