By what percentage pressure of a gas has to be changed to decrease its volume by 20% at constant temperature

apply Boyles law  PV=constant;⇒P1V1=P2V2let V1=100 then V2=100-20=80P2V2=P1V1⇒⇒P2P1=V1V2⇒P2P1=10080⇒P2P1=54                 P2P1−1=54-1⇒ΔPP=14percentage change of pressure=ΔPP×100=14×100=25% increase