If 70% of (x - y) = 30% of (x + y) then what percent of x is y?

70% of (x - y) = 30% of (x + y)

 7(x - y) = 3(x + y)

 \(\frac{(x+y)}{(x-y)}\) =  \(\frac{7}{3}\)

By componendo and dividendo

\(\frac{x}{y}\)  = \(\frac{10}{4}\)  = \(\frac{5}{2}\)

 x = 5 and y = 2

Required percentage =\(\frac{2}{5}\) × 100 = 40%