Air is 21% oxygen by volume. Oxygen has a density of 1.31 g/L. What is the volume in liters of a room that holds enough air to contain 55kg of oxygen?

First divide the mass of oxygen by its density,

55 kg / 1.31 L = 42 liters

Now if V is the volume of the room, then 21% of this volume is oxygen.

This can be written as:

0.21 V = 42 liters

Divide both sides of the equation by 0.21 to get V

V = 42/0.21 liters

V = 200 liter