Two containers of equal volume contain the same gas at pressures P1 and P2 and absolute temperatures T1 and T2 respectively. On joining the vessels, the gas reaches a common pressure P and common temperature T. The ratio P/T is equal to
(a) P1/T1 + P2/T2
(b) P1T1 + P2T2/(T1 +T2)
(c) P1T2 + P2T1/(T1 + T2)
(d) P1/2T1 + P2/2T2