chemistry
posted by sandra .
a 5.0 dm3 sample of oxygen at a pressure of 200 kPa and 2.0 dm3 sample of nitrogen at a pressure of 500 kPa are introduced into a 2.5 dm3 vessel.
what is the total pressure in the vessel?

There may be an easier way to work this problem but I would do the following:
Use PV = nRT and solve for n for oxygen.
Use PV = nRT and solve for n for nitrogen.
noxygen + nnitrogen = total n.
Then PV = nRT, substitute the new volume and solve for total P. There is no T listed in the problem but you can use any T you wish as long as the same T is used throughout.