A flask contains two gases: the first gas has a pressure of 0.75 atm and the second gas has a pressure of 485 atm. ?

Are you sure that the second pressure is 485 atm? If so, the total pressure is 485+0.75 = 485.75 atm which you would round to 486 atm

If the second pressure was actually 485 torr, then:
485/760 = 0.64 atm 
Total pressure = 0.64 + 0.75 = 1.39 atm...Show more