Helium has molar mass 4 g/mol and oxygen 32 g/mol. At the same temperature, set how many times faster the root-mean-square speed of helium is than that of oxygen.

2.83 (answers within ±0.25 count)

Both gases share the same average kinetic energy, so $u \propto 1/\sqrt{M}$ and the ratio is $\sqrt{32/4} = \sqrt{8} = 2.83$. Helium is not eight times faster, the square root matters, and getting it wrong is the standard error here.