Answer:
b. 16%
Step-by-step 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 deviation of the mean.
99.7% of the measures are within 3 standard deviations of the mean.
In this problem, we have that:
Mean = 500
Standard deviation = 100
Percentage of students who scored less than 400:
400 = 500 - 1*100
So 400 is one standard deviation below the mean.
The normal distribution is symmetric, which means that 50% of the measures are below the mean and 50% are above.
Of those who are below, 68% are within 1 standard deviation of the mean, that is, between 400 and 500. So 100-68 = 32% are below 400.
0.5*0.32 = 0.16 = 16%
So the correct answer is:
b. 16%
