The frequency for 10 < t £ 20 is 20 
The estimated mean length of a call is about 7·6 minutes 
The frequency density for 1 < t £ 3 is 8 
The frequency density scale goes up in twos 

The total number of calls is 16 
The modal group is 10 < t £ 20 
The median length of a call lies in the group 5 < t £ 10 
The frequency for 3 < t £ 5 is 4 
The frequency density for 5 < t £ 10 is 45 
There were 61 calls in total 
The frequency density for 5 < t £ 10 is 3 
The frequency for 10 < t £ 20 is 5 
