If a/1 = b/13 = c/7 then find ( (a + b )/(a + b + c ) ).

Given, \(\frac{a}{1}\) = \(\frac{b}{13}\) = \(\frac{c}{7}\)

Here we can directly conclude that 

a = 1, b = 13, c = 7, hence

⇒ (\(\frac{a + b }{a + b + c }\)) = (\(\frac{1 + 13}{1 + 13 + 7 }\)) = \(\frac{2}{3}\)