ogoluwa

I just came across a problem where they state that 99% of the observations are within the interval 200 and 400. Calculate the standard deviation, given a normal distribution.

Solution:

Mean:
(400+200)/2 = 300

Standard deviation = (400-300)/3


The solution doesn't take 2.58, rather it considers 3 standard deviations.

Which one do we choose on the exam: 2.58 or 3.