The Batteries Used by a Calculator Have Useful Lives That

Multiple Choice

The batteries used by a calculator have useful lives that follow a Normal distribution, with an average life of 2000 hours and a standard deviation of 200 hours. In the production process, the manufacturer draws random samples of 100 batteries and determines the mean useful life of the sample. What is the standard deviation _x of this mean?

A) 25 hours
B) 100 hours
C) 2 hours
D) 20 hours