Reduce fractions to a common denominator

1. Reduce fractions to a common denominator

2. Review1: 1)Write down 3 fractions in their simplest form with a denominator of 8. 2)Write down 3 fractions in their simplest form with a denominator of 9. 3)Simplify the following fractions:

3. 3 2 4 5 3 5 9 9 7 7 4 6 Review2: Comparing fractions: < >

4. 3 5 4 6 Thinking We need a commom denominator to compare these fractions.

5. 10 5×2 3×3 3 5 5 3 9 = = = = 12 12 6 4 4 6 4×3 6×2 commom denominator < So

6. Concept Find the LCD! Equivalent fractions Different denominators Common denominators

7. Review2: Finding the Least Common Multiple (LCM): LCM =12 3,4 6,12 6,9 3,4,8 5,10,20 LCM =12 LCM =18 LCM =24 LCM =20

8. Review3: Making equivalent fractions: ×4 ×3 ×2 12 6 12 ×2 ×3 ×4

9. Example 1: Reduction of fractions to a common denominator 12 Step 1:Find the LCD(LCM) Step 2:Write the equivalent fractions

10. Example 1: Reduction of fractions to a common denominator 12 Step 1:Find the LCD Step 2:Write the equivalent fractions

11. Example 1: Reduction of fractions to a common denominator 24 Step 1:Find the LCD Step 2:Write the equivalent fractions

12. correct： Improve： Correcting: ⑵ ⑶ ⑴ √ ？ ( ) × ( ) ( ) Any common denominator could be used. But the Least Common Denominator(LCD) makes the computation easier.

13. Exercise 1: Reduction of fractions to a common denominator Click here to see what you can do now--->

14. comparing: Addition: Substraction:

15. Exercise 2: Reduction of fractions to a common denominator

16. summary How to reduce fractions to a common denominator? Step 1:Find the LCD(LCM) Step 2:Write the equivalent fractions