EXAMPLE 3.1.14

The table below gives an accurate portrayal of the distribution of humans according to IQ.

1. What percent of humans have IQs greater than or equal to119?

A. 90

B. 99

C. 9

D. 10

SOLUTION

Since an IQ score of 119 has a percentile rank of 90, we know (according to the definition of percentile rank) that 90% of humans have IQs that are less than 119. This means that the other 10% must have IQs that are greater than or equal to 119. The correct choice is D.

2. Approximately what percent of humans have IQs between 92 and 104?

A. 30

B. 50

C. 20

D. 10

SOLUTION

The table shows us that 30% of people have IQs that are less than 92 (because an IQ of 92 has a percentile rank or 30). Likewise, the table shows that 60% of people have IQs that are less than 104. Now we subtract:

60% - 30% = 30%.

This tells us that 30% of people have IQs that are less than 104 but greater than or equal to 92. The best choice is A.

3. What percent of humans have IQs less than 87?

A. 24

B. 20

C. 14

D. 10

The fact that an IQ of 87 has a percentile rank of 20 means that 20% of people have IQs that are less than 87. The correct choice is B.