The National Assessment of Educational Progress (NAEP) includes a mathematics test for eighth-graders. Scores on the test range from 0 to 500. Suppose that you give the NAEP test to an SRS of 1225 eighth-graders from a large population in which the scores have mean = 281 and standard deviation = 127. The mean x will vary if you take repeated samples. The sampling distribution of x is approximately Normal. It has mean = 281. What is its standard deviation? (Round your answer to three decimal places.)