i dont know itanswer:
The normal distribution has two parameters:
The standard deviation .
It can be called .
The 68-95-99.7 rule indicates that:
68% of the measures are within 1 standard deviation of the mean.
95% of the measures are within 2 standard deviations of the mean.
99.7% of the measures are within 3 standard deviations of the mean.
In this problem, we have that:
This means that the middle 68% of people in this group score on the test are in the range of 120-20 = 100 to 120+20 = 140.