Question

A gas has a volume of 100.0 mL at a pressure of 780 mm Hg. what is the volume of the gas when its pressure is increased to 880 mm Hg?

Answer 1

The answer is 88.6 mL.

According to the Boyle's law pressure and the volume of a gas are inversely proportional at the constant temperature for a fixed mass:
P = k/V
or
P * V = k

So:
k = P1 * V1 = P2 * V2 = ...

We know that:
P1 = 780 mm Hg
V1 = 100 mL
P2 = 880 mm Hg
V2 = ?

780 * 100 = 880 * V2
V2 = 780 * 100 / 880
V2 =