sample standard deviation

For those using Kaplan – can someone explain why the book example on page 117 of book 1 takes the squared root of the sample variance to get your answer? On the question below … you are using the formula from the book. Trying to understand when to use the formula from the book vs simply taking the sq root.

A sample of returns for four randomly selected assets in a portfolio is shown below:

Asset Return (%)

A 1.3

B 1.4

C 2.2

D 3.4

A)

0.88%.

B)

1.13%.

C)

0.97%.