9.8 , 9.8 , 9.9 , 9.9 , 10.0 , 10.0 , 10.1 , 10.5
The mean and the standard deviation of the 8 numbers shown above is 10 and 0.212 respectively. What percent of the 8 numbers are within 1 standard deviation of the mean? Select.
A) 90.5 %  B) 87.5 %  C) 80.5 %  D) 77.5 %  E) 70.5 %

Rationale: within 1 standard deviation of the mean - means in the range { mean - 1 * sd ; mean + 1 * sd } = { 10 - 1 * 0.212 ; 10 + 0.3 } = { 9.788 ; 10.212 } . from the 8 listed numbers , 7 are within this range so 6 / 8 = 87.5 % . answer : b .
Answer: B