Robert is x years old.
Hannah is 7 years younger than Robert
The sum of their ages is 61.
How old are Hannah and Robert?

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.