The kinetic energy of a body is increased by 300%. The momentum of the body would increase by:

KE = $\frac{P^2}{2m}$       or $P^2 \propto KE$   ----(i)

$K{E}_2= K{E}_1+$ $\left(\frac{300}{100}\right)K{E}_1 = 4K{E}_1$

From (i) $\frac{P_2}{P_1} =$$\sqrt{\frac{K{E}_2}{K{E}_1}}$ = $\sqrt{\frac{4K{E}_1}{1K{E}_1}}$ = 2

It means momentum becomes twice, hence increase in momentum is 100%