how do you add -7/9 +3/7

0  Views: 255 Answers: 1 Posted: 10 years ago

-7/9 + 3/7

In order to add these two fractions, they must have a common denominator (9 and 7 are the denominators)  When I think of a fraction, I think of the denominator being the number of pieces one whole thing has (i.e.  the pie was cut into 9 pieces or 7 pieces).

The numerator is the number on top and to me represents how many of those pieces I have.  In 3/7, I have three of the seven pieces of the whole one thing.

In the other fraction, I am missing two pieces completely, and I owe the other seven pieces to someone else, meaning I have less than 0 pieces of the whole thing  (I know that is kinda "out there", but it makes sense to me).

I have to find a number that has both 7 and 9 as a multiple.  9, 18, 27, 36, 45, 54, 63 are multiples of 9.   7, 14, 21, 28, 35, 42, 49, 56, 63 are multiples of 7.  The first number that has both as a multiple is 63.  That will be my common denominator.

In order to get the /7 to 63, I had to multiply 7 x 9.  I need to multiply the 3 by 9, also, to keep my fraction "the same".   So 3/7 becomes 27/63.

Likewise, I had to multiply my denominator, 9, by 7.  I need to multiply the 7 by 7 also, again to keep my fraction "the same."  So -7/9 becomes -49/63.

NOW I can complete the equation by perfomring the addition.  The denominator will remain 63.  I need to add my numerators to find out how many pieces I have.  27 + (-49) = -22.   The answer to the qustion is      - 22/63.   This fraction is stated in its lowest possible terms.

I apologize for going into so much detail.  I love explaining math that is not too advanced.  I hope nobody thinks I think I am a know-it-all.  One thing I DO know is that I DON'T know everything!

banksizit

wow , a girl here with great looks and a great mind. NICE COMBO !!
Bob/PKB

You are really helping my day seem a lot better. THANK YOU

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