# Adding and Subtracting Fractions With different denominators.

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Adding and Subtracting Fractions With different denominators

Same Denominators 1 = 1 5 = 5 + (nothing changes) 3 = 3 5 = 5 4 Answer is--------  5 It is 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.

Reviewing Simplification “AAA MATH” Practice Link to site In an earlier lesson, you learned how to simplify, or reduce fractions by finding an equivalent, or equal, fraction where the numerator and denominator have no common factors.  Lets review

LCM What Does the following term mean? “Least common multiple” ?

Common denominator 1 4 = ? + 3 5 = ? 4 and 5 are not the same but …. they do have a “least common denominator” How do we know what it is ?

Least common Multiple 4 5 8 10 12 15 16 20 20 25 24 30 How do we find the “least common multiple” ? First:  We list their multiples

Question Did you see the LCM? ( Should I go Back )

AHH..HHAHH !! ( Sound effect )

SURVEY SAYS You are Correct !!

You are the bomb!!! 4 5 8 10 12 15 16 20 20 25 24 30 You saw the 20! this is the “least common multiple” And because we are working with fractions this 20 “LCM” is also the: “ LCD” “ Least Common Denominator” !!

Unlike Denominators 1 (multiply the 1 by 5 ) = 5_ 4 (multiply the 4 by 5 ) = 20 + 3 (multiply the 3 by 4) = 12 5 (multiply the 5 by 4) = 20 17! Answer is--------  20!  (see problem) (you cant change the value of a fraction.) When you change the denominator to 20 - you just changed the bottom of the fraction,. Now you must do the same thing to the top.

Good Work! Now lets Practice the skill !

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