Data was collected for 231 randomly selected 10 minute intervals. For each ten-minute interval, the number of people entering the atrium of a large mall were recorded. The data is summarized in the table below.

Number

of GuestsFrequency

100 - 119. 67

120 - 139 81

140 - 159. 15

160 - 179 21

180 - 199. 47

What is the class width for this GFDT?

Class width =