The mean of the data for the resting heart rate of adults is 69 beats per minute, and the standard deviation is 4 beats per minute. The results of the data were normally distributed.

Question

About what percentage of the population has a resting heart rate between 77 and 81?

Answer 1

z₇₇ = (77 - 69) / 4, or 2 → 97.72%

z₈₁ = (81 - 69) / 4, or 3 → 99.87%

What is the difference?