The standard deviation of n numerical data $x_1,x_2,x_3,...,x_n$, With mean $\overline{x}$ is equal to $\sqrt{\frac{S}{n}}$, where S is the sum of the squared differences $(x_i- \overline{x})^2$, for $1 ≤ i ≤ n$.

Each book that a bookstore sold last year was either new or used. The bookstore sold new books for $80 each and used books for $40 each. The standard deviation of the prices of the books sold last year was $16.

Quantity A	Quantity B
The fraction of the books sold last year that were new	$\frac{1}{2}$