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

A.

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