Statistical Estimation

Question

There is an example problem in my book that doesn't explain how they got to this answer:

sample: $217$ sample mean: $132.5$ standard deviation: $10$

"The $95$ part of the $68-95-99.7$ rule for Normal distributions says that $x$ is within $1.4$ cm of the mean in $95\%$ of all samples."

Where did $1.4$ come from? How do I calculate this number from the information above?

(Because I thought that the standard deviations for that rule were either $1, 2$ or $3$ and the book does not explain where they got $1.4$ or how they got it).

Answer 1

Perhaps they use the rule to mean you are 2 std deviations away from the mean, which is approximately $$ \frac{2 \sigma}{\sqrt{N}} = \frac{20}{\sqrt{217}} \approx 1.4 $$