2. Adding and Subtracting Fractions With different denominators

3. Different Denominators  It's easy to add and subtract like fractions, or fractions with the same denominator. –You just add or subtract the numerators and keep the same denominator.  To do this, you need to know how to find the least common denominator.  In an earlier lesson, you learned how to simplify, or reduce, a fraction by finding an equivalent, or equal, fraction where the numerator and denominator have no common factors. –To do this, you divided the numerator and denominator by their greatest common factor.  Next we will learn that you can also multiply the numerator and denominator by the same factor to make equivalent fractions.

4. L C D Since only like fractions can be added or subtracted, we first have to convert unlike fractions to equivalent like fractions. Since only like fractions can be added or subtracted, we first have to convert unlike fractions to equivalent like fractions. We want to find the smallest, or least, common denominator, because working with smaller numbers makes our calculations easier. We want to find the smallest, or least, common denominator, because working with smaller numbers makes our calculations easier. The least common denominator, or LCD, of two fractions is the smallest number that can be divided by both denominators. The least common denominator, or LCD, of two fractions is the smallest number that can be divided by both denominators.

5. Methods for Finding LCD The first method is to simply start writing all the multiples of both denominators, beginning with the numbers themselves. Here's an example of this method. Multiples of 4 are 4, 8, 12, 16, and so forth (because 1 × 4=4, 2 × 4=8, 3 × 4=12, 4 × 4=16, etc.). The multiples of 6 are 6, 12,…--that's the number we're looking for, 12, because it's the first one that appears in both lists of multiples. It's the least common multiple, which we'll use as our least common denominator.

6. Adding like Denominators Just simply add the top 2 numbers of the fractions together since they have common denominators.

7. Subtracting Like Denominators Subtracting Like Denominators Subtracting like denominators is just as easy as adding them! All you have to do is subtract the numerators and keep the same common denominator 3/4 – 1/4 = 2/4 4/6 - 1/6 = 3/6 7/9 – 1/9 = 6/9 5/9 – 3/9 = 2/9

8. Adding Unlike Denominators Find the least common denominator between 12 and 16 which is 48. Then find out what number times 12 is equal to 48 and do the same for 16 (3). Multiply 3 by both of the numerators, and then add the fractions!

9. Subtracting Unlike Denominators The least common denominator between 3 and 12 is 12 Find what number times 3 is equal to 12 and then multiply that by 1 Then simply subtract the numerator

10. HYPERLINKS Visit these websites below to learn more about fractions http://www.kidsolr.com/math/fractions.ht ml http://www.aaamath.com/B/fra.htm http://www.aaamath.com/fra410a- addfractld.html

11. GAME Go to http://www.aaamath.com/fr a66l-subfracud.html to play the online fraction game! http://www.aaamath.com/fr a66l-subfracud.html Click start and then solve the subtraction problem, and then report your score at the end!

12. YOU DID IT! NOW YOU ALL KNOW YOUR FRACTIONS!