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 first decile coincided with an IQ of
A) 75
B) 90
C) 100
D) 130

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 first decile coincided with an IQ of
A) 75
B) 90
C) 100
D) 130

Quizplus · Accepted Answer

The first decile (10th percentile) marks the point below which 10% of the observations fall. Given that 80% of the group is between IQs of 75 and 125, and the distribution is mesokurtic (indicating a normal distribution shape), the lower 10% would fall below 75, making 75 the closest boundary for the first decile.

A Researcher Gives IQ Tests to a Large Group of Adults