The standard deviation of n numerical data $$ x_{1}, x_{2}, x_{3}, ..., x_{n}$$, With mean $$\bar{x}$$ is equal to $$\sqrt{\frac{S}{n}}$$, where S is the sum of the squared differences $$(x_{i}-\bar{x})^{2}$$, 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
The fraction of the books sold last year that were new
Quantity B
$$\frac{1}{2}$$
