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Adding and Subtracting Fractions

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Adding and Subtracting Fractions With different denominators – PowerPoint PPT presentation

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Title: Adding and Subtracting Fractions


1
Adding and Subtracting Fractions
  • With different denominators

2
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.

3
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.


4
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.

5
Adding like Denominators
  • Just simply add the top 2 numbers of the
    fractions together since they have common
    denominators.


6
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
7
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!
8
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

9
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

10
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!

11
  • YOU DID IT! NOW YOU ALL KNOW YOUR FRACTIONS!
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