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Adding and Subtracting Fractions

- With different denominators

Different Denominators

- It's easy to add and subtract like fractions, or

fractions with the same denominator. - You just add or subtract the numerators and keep

the same denominator. - To do this, you need to know how to find the

least common denominator. - In an earlier lesson, you learned how to

simplify, or reduce, a fraction by finding an

equivalent, or equal, fraction where the

numerator and denominator have no common factors.

- To do this, you divided the numerator and

denominator by their greatest common factor.

- Next we will learn that you can also multiply the

numerator and denominator by the same factor to

make equivalent fractions.

L C D

- Since only like fractions can be added or

subtracted, we first have to convert unlike

fractions to equivalent like fractions. - We want to find the smallest, or least, common

denominator, because working with smaller numbers

makes our calculations easier. - The least common denominator, or LCD, of two

fractions is the smallest number that can be

divided by both denominators.

Methods for Finding LCD

- The first method is to simply start writing all

the multiples of both denominators, beginning

with the numbers themselves. Here's an example of

this method. Multiples of 4 are 4, 8, 12, 16, and

so forth (because 1 44, 2 48, 3 412, 4

416, etc.). The multiples of 6 are 6,

12,--that's the number we're looking for, 12,

because it's the first one that appears in both

lists of multiples. It's the least common

multiple, which we'll use as our least common

denominator.

Adding like Denominators

- Just simply add the top 2 numbers of the

fractions together since they have common

denominators.

Subtracting Like Denominators

- Subtracting like denominators is just as easy as

adding them! All you have to do is subtract the

numerators and keep the same common denominator

3/4 1/4 2/4 4/6 - 1/6 3/6 7/9 1/9

6/9 5/9 3/9 2/9

Adding Unlike Denominators

Find the least common denominator between 12 and

16 which is 48. Then find out what number

times 12 is equal to 48 and do the same for 16

(3). Multiply 3 by both of the numerators, and

then add the fractions!

Subtracting Unlike Denominators

- The least common denominator between 3 and 12 is

12 - Find what number times 3 is equal to 12 and then

multiply that by 1 - Then simply subtract the numerator

HYPERLINKS

- Visit these websites below to learn more about

fractions - http//www.kidsolr.com/math/fractions.html
- http//www.aaamath.com/B/fra.htm
- http//www.aaamath.com/fra410a-addfractld.html

GAME

- Go to http//www.aaamath.com/fra66l-subfracud.html

to play the online fraction game! - Click start and then solve the subtraction

problem, and then report your score at the end!

- YOU DID IT! NOW YOU ALL KNOW YOUR FRACTIONS!