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Adding and Subtracting Unlike Fractions

Adding and Subtracting Unlike Fractions. Lesson 5.2. Reading a Diagram. If the diagram has two rows that are even, it is an addition problem. The addition problem is found in the top row. The answer is found in the bottom row. Example. The top row is “one half plus one fourth”. 1 2. 1 4.

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Adding and Subtracting Unlike Fractions

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  1. Adding and Subtracting Unlike Fractions Lesson 5.2

  2. Reading a Diagram • If the diagram has two rows that are even, it is an addition problem. • The addition problem is found in the top row. • The answer is found in the bottom row.

  3. Example The top row is “one half plus one fourth” 1 2 1 4 The bottom row holds the answer: Count up the fourths. We have three fourths. 1 4 1 4 1 4

  4. Subtracting With a Diagram • If the top row and bottom row is uneven, then it is a subtraction problem. • Think of it as the top row minus the bottom row.

  5. Example 1 12 1 12 1 12 1 12 1 12 1 4 This problem says: 5/12 - 1/4 Cancel out the one fourth, and the same amount on the top row. Count what is left: two twelfths. When you reduce 2/12, you get 1/6.

  6. Most problems will be solved with pencil and paper. • List the multiples of both denominators. • Find the least common multiple (LCM). • Write new fractions with the LCM as the new denominator. • Find the factor you multiply by to get from your original denominator to your new denominator. • Use that same factor, and multiply it by your original numerator to get a new numerator.

  7. WHAT DOES THAT MEAN? Let’s illustrate the steps with an example. 3 1 + 4 6

  8. 3 1 + 4 6 9 2 x 3 x 2 + 12 12 11 Multiples of 4: 4, 8, 12, 16, 20 12 Multiples of 6: 6, 12, 18, 24, 30

  9. Example 2 9 2 10, 20, 30, 40, 50 5, 10, 15, 20, 25 5 10 5 x 1 x 2 9 4 = 10 10 10 1 = 2

  10. Homework Time!

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