1. Lesson – Finding the Least Common Multiple (LCM)
Steps:
Write out the multiples of the first number.
Write out the multiples of the second number.
Find the smallest multiple that both numbers have in common.
Example:
4: 4, 8, 12, 16, 20, 24
5: 5, 10, 15, 20
LCM: 20
Example:
2: 2, 4, 6, 8, 10, 12, 14, 16
8: 8
LCM: 8
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2. Lesson - Adding Fractions with Unlike Denominators
Step:
Determine the denominators
Find the least common multiple (LCM).
Your least common multiple will become your least common denominator (LCD).
Generate Equivalent Fractions using the LCM as the LCD.
Add or Subtract Fractions.
Example: 1.
LCM:
3: 2, 4, 6, 8, 10, 12
4: 4, 8, 12
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3. Lesson - Subtracting Fractions with Unlike Denominators
Step:
Determine the denominators
Find the least common multiple (LCM).
Your least common multiple will become your least common denominator (LCD).
Generate Equivalent Fractions using the LCM as the LCD.
Add or Subtract Fractions.
Example: 1.
LCM:
2: 2, 4, 6
4: 4
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4. Adding & Subtracting Fractions
The
‘Butterfly’ Method
Copyright © 1999 Lynda Greene

6. The “Butterfly” is a short-cut method used for adding & subtracting any two fractions. The usual method is called finding a “Common Denominator”
Copyright © 1999 Lynda Greene

7. Adding and Subtracting Fractions
Make the denominators the same. (Multiply them by each other)
Multiply the numerator by the other fractions denominator.
Add or subtract across.

8. Fractions: The Butterfly Method
2 x 5
4 x 3 +
Step 1:
Draw the wings
Copyright © 1999 Lynda Greene

9. Fractions: The Butterfly Method+
3 x 5 = 15
Step 2:
Multiply the denominators
Copyright © 1999 Lynda Greene

10. Fractions: The Butterfly Method
2 x x 3 +
= 22
3 x 5 = 15
Step 3:
Compute the new numerators using the
Sign in the middle of the 2 fractions.
Copyright © 1999 Lynda Greene

11. Fractions: The Butterfly Method
2 x x 3 22 + 15
Step 4:
Simplify the new fraction (answer).
Copyright © 1999 Lynda Greene

12. Practice Problems 1. 2. 3.
Copyright © 1999 Lynda Greene

13. Try These A D E B F C

14. Try These 10 9 17 27 A D 41 28 13 12 B E 19 20 26 21 C F