Number of collisions per unit time of molecules of gas on the wall a container per unit area will 

Number of collisions per unit area per unit time 

$\begin{array}{l}\frac{1}{\text{ time between two collision }\times \text{ area }}\\ \Rightarrow \mathrm{n}/\mathrm{A}\propto \frac{{\mathrm{v}}_{\mathrm{rms}}}{\text{ dis tance between walls }\times \mathrm{A}}\\ \Rightarrow {\mathrm{v}}_{\mathrm{rms}}\propto \sqrt{\mathrm{T}}\end{array}$

distance between walls $x A =$ volume

So $\frac{n}{A}\propto \frac{T^{1/2}}{V}$$\propto \frac{P}{\sqrt{T}}$

if both T and V are halved,  $\frac{n}{A}$ increases.Also if both P and T are doubled , $\frac{n}{A}increases .$