A researcher gives IQ tests to a large group of adults, and discovers that the
mean, median and mode all equal 100. The highest score in the group was 130
and the lowest was 70. Between IQ's of 75 and 125, 80% of the group was found, and 50% were found between IQ's of 90 and 110. The shape of the graphed distribution was mesokurtic.
-The interdecile range was equal to
A) 60
B) 50
C) 20
D) 0

Question

A researcher gives IQ tests to a large group of adults, and discovers that the 
mean, median and mode all equal 100.  The highest score in the group was 130 
and the lowest was 70.  Between IQ's of 75 and 125, 80% of the group was found,  and 50% were found between IQ's of 90 and 110.  The shape of the graphed  distribution was mesokurtic.     
-The interdecile range was equal to
A) 60
B) 50
C) 20
D) 0

Quizplus · Accepted Answer

Since the interdecile range is the difference between the 90th percentile and the 10th percentile, and we know that 80% of the group falls between IQ's of 75 and 125, the 10th percentile is 75 and the 90th percentile is 125. Therefore, the interdecile range is 125-75 = 50.

A Researcher Gives IQ Tests to a Large Group of Adults