Run $V = nRT/P$ once at STP — standard temperature and pressure, $0\,^\circ\mathrm{C}$ (273 K) and 101.325 kPa — and out falls a number worth memorizing: one mole of ANY ideal gas rents $22.4\ \mathrm{L}$. Helium, oxygen, carbon dioxide — same rent, because ideal gas particles are all equally standoffish regardless of their size. So at STP the whole law collapses to $V = n \, V_m$ with $V_m = 22.4\ \mathrm{L/mol}$, read aloud: V equals n V-m.

Now the fine print, which is where exams hunt: 22.4 is a promise made ONLY at STP. A warm room, a pressurized cylinder — the shortcut's contract is void, and $PV = nRT$ collects the full fare. Before you reach for 22.4, check the conditions like you would check a coupon's expiry date. This lesson makes sure you do.