$$\text { TABLE 3-7 }$$ Given Below Is the Frequency Distribution of the 12-Month Rate

$$\text { TABLE 3-7 }$$ Given below is the frequency distribution of the 12-month rate of return achieved by 30 stocks.
$\begin{array}{cc}\hline \begin{array}{c}\text { 12- month Rate of Return} \\\end{array} & \text { Number of Funds } \\\hline-0.10 \text { but less th an } 0.0 & 3 \\0.0 \text { but less th an } 0.1 & 5 \\0.1 \text { but less th } 0.2 & 6 \\0.2 \text { but less th } 0.3 & 10 \\0.3 \text { but less than } 0.4 & 6 \\\hline\end{array}$

-Referring to Table 3-7, what is the approximate standard deviation?