Why can't standard deviation be negative?

Before a new phone system was installed, the amount a company spent on personal calls followed a normal distribution with an average of $900 per month and a standard deviation of $50 per month.

Mrs. Cochran made chocolate fudge brownies during vacation. She took 4/12 of the brownies to school to share with the teachers. At dinner, her family ate 5/12 of the brownies. What fraction of brownies was left after dinner.

Given the equation, D=m/v if D=6/7 and = m+3 then m=. A. 18 B.-18 C. 15

Find the area of a sector with a central angle of 102 degrees and a radius of 15.7 millimeters.

Marlin is two years older than reese, and the same age as lee. if lee is 12, how old is reese

Which expression is equivalent to (5x^3) (4x) ^3?

The graph shows that f (x) = (one-third) Superscript x is translated horizontally and vertically to get the function (one-third) Superscript x minus h. On a coordinate plane, 2 exponential functions are shown.

Maggie is painting the exposed areas of a cement figure that is being placed at the park. How many square feet will she need to cover with paint?

A cheetah can run 70 mph what is the speed in feet per hour

The average person loses about 8x10 strands of hair each day about how many strands o hair can you lose in 9 days?