Juan makes a measurement in a chemistry laboratory and records the result in his lab report. The standard deviation of students' lab measurements is σ = 10 milligrams. Juan repeats the measurement 3 times and records the mean x of his 3 measurements. (a) What is the standard deviation of Juan's mean result? (That is, if Juan kept on making 3 measurementand averaging them, what would be the standard deviation of all his x 's?)