Answer:
So about 95 percent of the observations lie between 480 and 520.
Explanation:
The Empirical Rule states that, for a normally distributed random variable:
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:
The mean is 500 and the standard deviation is 10.
About 95 percent of the observations lie between what two values?
From the Empirical Rule, this is from 500 - 2*10 = 480 to 500 + 2*10 = 520.
So about 95 percent of the observations lie between 480 and 520.