:3b. In a Public Health Service Study of 1964, a histogram was
plotted showing the number of cigarettes per day smoked by each
subject (male, current smokers), as shown in diagram ? on page ?
of the test.  The density is marked in parentheses.  The class
intervals include the right endpoint, not the left.

:

 a.  1.5%
 b.  15%
 c.  30%
 d.  50%
 e.  70%

(There are twenty cigarettes in a pack.)