Question

what is the partial pressure of N2 in the mixture of N2 and O2 having a total pressure of 1075 torr if the partial pressure of O2 is 720 torr?

Answer 1

Dalton's law of partial pressures tells us Ptotal = sum of partial pressures or
Ptotal = PN2 + PO2. You know Ptotal and PO2. Looks simple enough to solve for PN2