Answer
$\therefore$ He effuses 3.16 times as fast as Ar.
Work Step by Step
$Rate\propto \frac{1}{\sqrt M}$
Since Ar (40) has a higher Molecular weight than He(4)
$\frac{Rate_{He}}{Rate_{Ar}}$ = $\frac{\sqrt 40}{\sqrt 4}$
$\frac{Rate_{He}}{Rate_{Ar}}$ = $\sqrt 10$
$\frac{Rate_{He}}{Rate_{Ar}}$ = $ 3.16 $
$\therefore$ He effuses 3.16 times as fast as Ar.
