1， 9.4, 9.9, 9.9, 9.9, 10.0, 10.2, 10.2, 10.5

the mean and the standard deviation of the 8 numbers shown are 10 and 0.3, respectively. what persentage of the 8 number's are within 1 standard deviation?

A) 90% B) 85% C) 80% D) 75% E) 70%

第一题,10-0.3=9.7 10+0.3=10.3 the number within 1 standard deviation should be between 9.7-10.3 so there are six numbers within 1 standard deviation 6/8=75%

why the the number within 1 standard deviation should be between 9.7-10.3 . what is the meaning of 1 standard?