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 = 13 milligrams. Juan repeats the measurement 5 times and records the mean x¯¯¯ of his 5 measurements. (a) What is the standard deviation of Juan's mean result? (That is, if Juan kept on making 5 measurements and averaging them, what would be the standard deviation of all his x¯¯¯′s?) (b) How many times must Juan repeat the measurement to reduce the standard deviation of x¯¯¯ to 2.6?