Answer:
about 9.91
Explanation:
You want the standard deviation of the given data set:
{138, 129, 145, 134, 142, 159, 153, 142, 127}
Standard deviation
The standard deviation can be found by a suitable calculator, or by working through the formula.
mean = (∑x)/9 = 1269/9 = 141
mean square = (∑x²)/9 = 179813/9 = 19,979.2222...
σ = √((mean square) -mean²) = √98.2222...
σ ≈ 9.91
The standard deviation of this dataset is about 9.91 units.