At constant temperature, a gas is at a pressure 1080 mm Hg. If the volume is decreased by 40%, find the new pressure of the gas.

V₁ = Initial volume of the gas = V

P₁ = Initial pressure of the gas = 1080 mm of Hg

V₂ = Final volume of the gas = decreased by 40%
= 60% of V₁ = $\dfrac{60}{100}$V = $\dfrac{3}{5}$V

P₂ = Final pressure of the gas = ?

By Boyle's Law:

$\text{P}$1 \text{V}1 = \text{P}2 \text{V}2

Substituting the values :

$\text{V} \times 1080 = \text{P}$2 \times \dfrac{3}{5}\text{V} \\[0.5em] \text{P}2 = \dfrac{5\times 1080 }{3} \\[0.5em] \text{P}_2 = 1800 \text{ mm of Hg}

∴ Final pressure = 1800 mm of Hg