Question 728518
5/9 + 1/12 
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Cross multiply, similar to equations
= (N1*D2 + N2*D1)/D1*D2 N = Numerator, D = Denominator
= (5*12 + 1*9)/(9*12
= 69/108
= 23/36
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Conventional method:
Find a common denominator.  The product always works
5/9 + 1/12 = 60/108 + 9/108
= 69/108
etc
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Don't waste time fretting about the LCD, the Least Common Denominator.