Finding the Least Common Denominator to Add/Subtract Fractions

Make a ratio table for each fraction. 1 6 3 4

Skip Count by 1 1 2 6 3 4

1 2 3 6 3 4

1 2 3 4 6 3 4

1 2 3 4 5 6 3 4

Skip Count by 6 1 2 3 4 5 6 12 3 4

1 2 3 4 5 6 12 18 3 4

1 2 3 4 5 6 12 18 24 3 4

1 2 3 4 5 6 12 18 24 30 3 4

1 2 3 4 5 6 12 18 24 30 Skip Count by 3 3 6 4

1 2 3 4 5 6 12 18 24 30 3 6 9 4

1 2 3 4 5 6 12 18 24 30 3 6 9 12 4

1 2 3 4 5 6 12 18 24 30 Skip Count by 4 3 6 9 12 4 8

1 2 3 4 5 6 12 18 24 30 3 6 9 12 4 8

1 2 3 4 5 6 12 18 24 30 3 6 9 12 4 8 16

Look at the 2nd row in each ratio table. 1 2 3 4 5 6 12 18 24 30 3 6 9 12 4 8 16

Find the number each row has in common. 1 2 3 4 5 6 12 18 24 30 3 6 9 12 4 8 16

These are the 2 fractions you will add. 1 2 3 4 5 6 12 18 24 30 3 6 9 12 4 8 16

2 12 + 9 12 1 2 3 4 5 6 12 18 24 30 3 6 9 12 4 8 16

Add the numerators 2 + 9 2 + 9 = 11 2 12 + 9 12

2 12 + 9 12 Add the numerators 2 + 9 2 + 9 = 11 2 12 + 9 12 The denominator doesn’t change.

So….. 2 12 + 9 12 = 11 12