Find the single pass and overall conversion of CO

Carbon monoxide and hydrogen react to form methanol. However nitrogen is often added as an inert. 100 moles that contains 4 mol% nitrogen and the rest CO and H₂ in stoichiometric proportions enter the reactor. The effluent leaves the reactor where the methanol is condensed and removed. The remaining gases leave the condenser where 25 % are released as a purge and the rest recycles to join the fresh feed. If the N₂ leaving the reactor is 5% of that stream, find the single pass and overall conversion of CO. What would the single pass and overall conversion be without the purge? If the purge lowers the overall conversion, why would you include it?