How much pressure be increased be increased in order to decrease the volume of a gas by 5% at a constant temperature? 

Pressure is inversely proportional to volume

 

Let P_o and V_o be the initial pressure and initial volume.

 

let P and V be the final pressure and final volume .

 

( P / P_o ) = ( V_o / V )  = 1/0.95

 

Hence P ≈ 1.053 P_o ;  Hence Pressure should be increased by 5.3%