:

 Income (thousands of dollars) Number of families

 0 - 20 15
 20 - 50 75
 50 - 100 60

Suppose you construct a percentage histogram with each horizontal
unit representing one thousand dollars.  Then the height of the
rectangle over the first class interval (the one from 0 to 20) is
equal to
 
 a.  0.5
 b.  1.0
     c.  1.5
   d.  2.0
 e.  2.5