help please

:confused: i've just started studing statistics and i want to use the chebychev's therorm, however i'm not sure how can i find the value of the standard deviation

this is the question"

a random sample of data has a mean of 75 and a variance of 25.

A- use chebychev's therorm to determine the percent of observtions between 65 and 85.

my answer was
K= standard deviation = √ (65 – 75)2 + (85 - 75) 2 / (2-1)
i'm not sure what is the value of n, is it 2-1 or 20-1??

= √200 = 14.14 1 – 1/k= 1- 1/14.14 = 92.92 %

B. if the data are mounded use the empirical rule to find the approximate percent of observations between 65 and 85.

i didn't understand the question i searched for n example in the book but nothing was clear. . any hints please


TS Contributor
The standard deviation is the square root of the variance, regardless of the shape of the distribution. Since the variance is 25, the std dev is 5. This should help tremendously with answering both questions....