Children living near a smelter were exposed tolead, and their IQ scores were subsequently measured. The histogram on the right was constructed from those IQ scores.

IQ scores of Sample of Children Exposed to Lead

0

40

80

120

160

0

10

20

30

40

IQscore

Frequency

A histogram is titled 'IQ scores of Sample of Children Exposed to Lead.' Its horizontal axis is labeled 'IQ score' from 0 to 160 in increments of 20 and its vertical axis is labeled 'Frequency' from 0 to 40 in increments of 10. The heights of the vertical bars of bin width 20 are as follows: 0 to 20, 0; 20 to 40, 7; 40 to 60, 12; 60 to 80, 34; 80 to 100, 20; 100 to 120, 5; 120 to 140, 1; 140 to 160, 0.

a. Estimate the frequency for each of the six score categories.

Category

20-39

40-59

60-79

80-99

100-119

120-139

Frequency

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nothing