3/7 of the students in a school are in sixth grade.
a. How many sixth graders are there if the school has 210 students?

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.