Question

18, 19, 21, 27, 20

Answer 1

$$mean=\mu=\dfrac{18+19+21+27+20}{5}=21$$

$$Var(X)=\sigma^2=\dfrac{9+4+0+36+1}{5}=10$$

$$\sigma=\sqrt{\sigma^2}=\sqrt{10}\approx3.1623$$