What is 3×3/4 and what is the strategy behind it

I believe the answer is 9.

When multiplying fractions, you have to multiply numerator by numerator and denominator by denominator. 3 is the same thing as 3/1.
3 x 3 = 9 
1 x 4 = 4

Therefore, the answer is 9/4 or 2 1/4.

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.