This is a question from an entrance test. I was trying to solve it but now, i am stuck in it. Question is :
If a data set is approximately normal with sample mean of 75 and standard deviation of 5, how many observations fall with 75 + or - 5?
The answer options were available in percentage.
Hint:
The key is knowing that the distribution is normal.
For the specific solution see, for instance: 68–95–99.7 rule.