## Lesson 2: Fractions II

October 17, 2010

**2.1. Finding the Lowest Common Denominator**

**To find the lowest possible common denominator of 2 or more fractions:**

**Simplify****the fractions**if possible**Find the Lowest Common Denominator,**which is the**Lowest Common Multiple**of all denominators.- To work out the
**new numerator**of each fraction**, divide the****Lowest Common Multiple****by each denominator and multiply the quotient by the corresponding numerator.**

** You can undertand the technique** on this link by clicking on the picture

http://www.ixl.com/math/practice/grade-8-least-common-denominator

**3. Comparing fractions**

To compare fractions we can work out their values (dividing numerator by denominator) and compare them or we can apply the following criteria:

- If the two fractions have the
**same denominator**, the**larger fraction is the fraction with larger numerator**. - If the two fractions have
**equal numerator and different denominators**, the**larger fraction is the fraction with smaller denominator**. - If the two fractions have
**different numerators and different denominators**we**reduce**them to their**Lowest Common Denominator**and we apply the criterion before.

Remember:

**Descending order** means from the largest to the smallest (or going down).

**Ascending order** means from the smallest to the largest (or going up).

Do you remember signs “>” and “<“?

**Sign > means greater ( 2 > 1 means “2 is greater than 1”) **

**Sign < means smaller ( 2 < 99 means “2 is smaller than 99”)**

Practise and play a funny game on

** **

You will find harder exercises on

**http://www.ixl.com/math/practice/grade-8-compare-rational-numbers**

**4. Operations**

**4.1. Adding or subtracting fractions**

** ****To** **add or subtract fractions with the same denominator** you have to do is to add or subtract the numerators.

And it is always a good idea to make your result “nice” by simplifying if possible.

** ****Example:**

Find |
1 |
+ | 2 |

5 |
5 |

Both fractions have the same denominator of 5, so we can simply add the numerators:

1 |
+ | 2 |
= |
3 |

5 |
5 |
5 |

** ****To** **add or subtract fractions** with **different denominators** we must first make the denominators the same (by finding the Lowest Common Denominator and using equivalent fractions), and finally add or subtract the new numerators and write the new denominator.

Remember, simplify if possible!

Here you can see examples step by step and progress by practising. In order to advance you have to click on the right arrow placed at the bottom of the screen.

Here you are a video on adding fractions very easy to understand

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