Pressure and volume of a gas are inversely related. As one goes up, the other goes down, and vice-versa. Pressing down on a bicycle tire pump illustrates that by decreasing the volume, squeezing the air into a smaller space, the pressure increases, and forces it through the hose into the tire. This inverse relationship is summarized by
Pressure = 1/Volume and Volume = 1/Pressure or
P= 1/V and V = 1/P
This relationship can be summarized as the pressure times volume of initial conditions is equal to the pressure times volume of the final conditions, or
(Pressure 1)(Volume 1) = (Pressure 2)(Volume 2)
Adding the variable of temperature causes the volume and pressure to increase or decrease as the temperature increases or decreases. The formula to describe that is a bit more complex, including n as the number of moles of the gas and R which is the gas constant:
(Pressure)(Volume) = (number of moles)(gas constant)(temp)
Their relationship is inverselly proportionated in some way, and affects the gas the same way.