I have a question. If we got an information and have to represent it by a bargraph why cant we do write just numbers.If its important than why cant we use a tally marks . our teacher said that if you use a bargraph thats good. Why its like that. Please do explain me.

If we have some information, then that information is best represented through graphical representation. It will take more time to see the numbers or the tally marks, but by just taking a look at the bar graph, we can immediately get the information represented by the bar graph. 

Therefore, it would be better if you represent the data that you have using a bar graph.