Heliox is a heliumoxygen mixture that may be used in scuba tanks for divers working at great depths. It is also used medically as a breathing treatment.

A 8.25 L tank holds helium gas at a pressure of 1258 psi. A second 8.25 L tank holds oxygen at a pressure of 334.5 psi. The two gases are mixed in a 8.25 L tank. If the temperature remains the same throughout the process, what is the pressure of the gas mixture in the tank? Assume ideal gas behavior.

= ?? psi