GENIUS PROFESSOR

The professor was collecting Rs. 250 each from the students. He made 4 columns, distinguishing three digits for numbers and one column for name of student. He wrote the name of student in one column and amount paid in three columns; thus 2 I 5 I 0. On completion of the task, he started adding the total at the end. There were 72 students, he made some mistake and the total was not tallying with the amount collected. He was puzzled. 

One student observed this and offered help. The professor handed over the sheet to the student. The student multiplied the number of students and the money collected.