The gas that a diver breathes must be maintained at a partial pressure of 0.20 atm of oxygen. More oxygen could poison the diver, and less would lead to suffocation. The total pressure, however, must be equal to the external pressure to avoid collapsing the lungs. A special valve is used to equalize the pressure inside the diver's lungs with the external pressure by adding helium gas. The valve also maintains oxygen levels by using Dalton's Law. If the total pressure in the cylinder is 1.00 atm, what is the pressure of the helium?