There were seven students at a lunch table. Four of the students finished and got up. There were three students left. Which number completes the equation? Seven minus the missing number equals three.
We know there were seven students to begin with. So we can write that down. We know this is a minus so we can requote the minus symbol. And we know that four of the students finished eating, got up, and left.
So we subtract the number of children who left. Seven minus four is three. This is the number of students who are left at the table. So the missing number that completes the equation is four.