a set of data is normally distributed with a mean of 100 and

a set of data is normally distributed with a mean of 100 and a standard deviation of 10. Almost all (more than 99%) values will be between

80 and 120

90 and 110

70 and 130

85 and 115

By empirical rule, this describes between 3 standard deviations below or above the mean.

thus,

u - 3*sigma = 100 - 3*10 = 70
u + 3*sigma = 100 + 3*10 = 130

Thus, it is OPTION C. [ANSWER]