The ratio of students in jamie's class to have a dog or cat home to those who don't is 12 to 8 what percent of the class do not have a cat or dog at home

Your answer would be 4% because if you subtract 8 from 12 you'd get 4.

The major difference is that a histogram is only used to plot the frequency of score occurrences in a continuous data set that has been divided into classes, called bins.  bar charts, on the other hand, can be used for a great deal of other types ofvariables  including  ordinal  andnominal  data sets.