SOLUTION: What number added to the numerator and denominator of the fraction 3/8 results in a fraction equal to 2/3?

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Question 638074: What number added to the numerator and denominator of the fraction 3/8 results in a fraction equal to 2/3?
Answer by MathLover1(20855) About Me  (Show Source):
You can put this solution on YOUR website!
%282%2Bx%29%2F%283%2Bx%29=3%2F8...cross multiply and solve for x
%282%2Bx%298=3%283%2Bx%29
16%2B8x=9%2B3x
8x-3x=9-16
5x=-7
highlight%28x=-7%2F5%29
check:
%282%2Bx%29%2F%283%2Bx%29=3%2F8
%282%2B%28-7%2F5%29%29%2F%283%2B%28-7%2F5%29%29=3%2F8

%28%282%2A5-7%29%2F5%29%2F%28%283%2A5-7%29%2F5%29=3%2F8

%28%2810-7%29%2Fcross%285%29%29%2F%28%2815-7%29%2Fcross%285%29%29=3%2F8
%2810-7%29%2F%2815-7%29=3%2F8
3%2F8=3%2F8