chemistry
posted by laura .
A fixed amount of gas initially at 100 K and pressure P1 is expanded from 1 L to 100 L in a piston. The temperature, T2, of the gas at this point is 50 K. The piston is then locked at constant volume V2=100 L and half the gas is pumped out at a constant temperature of T2 . The observed pressure, P3, after half the gas is removed under these conditions is 0.03 atm. What was the initial pressure, P1 ?

I would use PV = nRT and solve for n = numbr of moles of the gas at the third stage (you know P, V, R, and T)
Then double that amount to find moles at stage and solve for P2. Then I believe you can use (P1V1/T1) = (P2V2./T2) and solve for P at the first stage. 
I can't solve this question