Question 620872
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Hi,
Re TY, As to demominator {{{((1/a) + (1/b))}}}: 
Puting in terms of {{{(b+a)/ab)}}} (Using a common denominator)allows us to work together with the numerator more easily
{{{3/((1/a) + (1/b))= 3/((b+a)/ab) = 3ab/(a+b)}}}