Scores of adults aged 60 to 64 on a common IQ test are approximately Normally distributed with mean 90 and standard deviation 15.
The third quartile of the distribution of IQ scores of adults aged 60 to 64 is between
A) 90 and 105.
B) 105 and 120.
C) 90 and 75.
D) 60 and 75.

Question

Quizplus · Accepted Answer

The third quartile (Q3) of a normal distribution is the value below which 75% of the observations may be found. For a normal distribution, Q3 is typically found 0.675 standard deviations above the mean. Given a mean of 90 and a standard deviation of 15, Q3 = 90 + (0.675)(15) = 90 + 10.125 = 100.125, which falls within the range of 90 to 105.

Scores of Adults Aged 60 to 64 on a Common