# Under a normal curve mean $\pm 3\: \sigma$ covers an area equal to

$\begin {array} {1 1} (A)\;99.73 \% & \quad (B)\;95.45 \% \\ (C)\;75.15 \% & \quad (D)\;none\: of \: these \end {array}$

It covers 99.73 % of total area under normal curve.