Increase in denominator,decreases the fraction value by how much percent?

Let the fraction be y/x and the denominator be increased by a%.
Thus, the new fraction obtained is y/(x + x*a/100) = y/[x(1 + a/100)]
The percent decrease in the original fraction = $$\frac{y/x - y/[x(1 + a/100)]}{y/x}$$x100% = $$\frac{a}{100 + a}$$x100%