Question

If pressure of air is doubled then what is effect on speed of sound?

Answer 1

Your equation is $V=\sqrt{y}\frac{P}{\rho }$
Where
V= velocity
y= constant related to the type of gas
P = pressure
$\rho$ = density
Pressure and density are related for a perfect gas. If pressure doubles and the temperature stays the same, the density will double so the speed of sound will remain the same.
The interrelationship between pressure and density is derivable from PV = nRT. If the temperature remains constant then $P=\frac{C}{V}$, where C is a constant and V is volume.
Since density $\rho =\frac{m}{V}$
$P\alpha \frac{1}{V}P\alpha \rho$