The room was full of students. Then 47 students left the room. 22 students remained. How many students were there when the bell rang?

Question

math problem

Answer 1

ASSUMING that the reason for leaving was that the bell rang, you can figure out that 47 remained, and 22 left, you can bring them back (mentally) and add 22 to 47, to get the desired answer.  I hope that this total was not one class--that's too many to teach all at once!