1. Measurement Adding and Subtracting Fractions with Different Denominators

2.  We can add fractions with the same (common) denominator easily. Adding and Subtracting Fractions 3535 + 1515 4545 =

3.  We can add fractions with the same (common) denominator easily. Adding and Subtracting Fractions 3535 + 1515 4545 =

4.  We can also add fractions without the same denominators by using equivalent fractions to determine a common denominator. Adding and Subtracting Fractions 1414 + 1212 ? =

5.  Before we can add fractions, we need these numbers to be the same. Adding and Subtracting Fractions 1414 + 1212 ? =

6.  First:Check to see if the smaller will divide into the larger denominator.  If so: We only have to change one of the denominators. Adding and Subtracting Fractions 1414 + 1212 ? =

7.  Example: 2 will divide into 4, so we can use 4 as the common denominator Adding and Subtracting Fractions 1414 + 1212 ? =

8.  Multiply both the numerator and denominator by 2 Adding and Subtracting Fractions 1414 + 1212 ? = x2 1414 + 2424 ? =

9.  Multiply both the numerator and denominator by 2 Adding and Subtracting Fractions 1414 + 1212 ? = x2 1414 + 2424 = 3434

10.  What if: The smaller denominator will not divide into the larger denominator?  If not: We have to find a common multiple for a denominator. Adding and Subtracting Fractions 1414 + 1313 ? =

11.  Check the multiples of 3 and 4.  3 = 3, 6, 9, 12, 15, 18, 21, 24  4 = 4, 8, 12, 16, 20, 24 Adding and Subtracting Fractions 1414 + 1313 ? =

12.  12 is the lowest common multiple of 3 and 4  3 = 3, 6, 9, 12, 15, 18, 21, 24  4 = 4, 8, 12, 16, 20, 24 Adding and Subtracting Fractions 1414 + 1313 ? =

13.  To make the denominator of the first fraction 12, multiply both the numerator and denominator by 3. Adding and Subtracting Fractions 1414 + 1313 ? = x3 ? 12 +=

14.  To make the denominator of the first fraction 12, multiply both the numerator and denominator by 3. Adding and Subtracting Fractions 1414 + 1313 ? = x3 3 12 +=

15.  To make the denominator of the second fraction 12, multiply both the numerator and denominator by 4. Adding and Subtracting Fractions 1414 + 1313 ? = x4 3 12 + ? 12 =

16.  To make the denominator of the second fraction 12, multiply both the numerator and denominator by 4. Adding and Subtracting Fractions 1414 + 1313 ? = x4 3 12 + 4 12 =

17.  We can now add the two fractions. Adding and Subtracting Fractions 1414 + 1313 ? = 3 12 + 4 12 = 7 12

18.  Try this one: Adding and Subtracting Fractions 1313 + 2525 ? =

19. 1313 + 2525 ? = 5 15 + 6 15 ? = x5 x3

20. Adding and Subtracting Fractions 1313 + 2525 ? = 5 15 + 6 15 = x5 x3 11 15