Zachary did 22 push-ups in gym class today. David did 1 more push-ups than Zachary. John did 20 push-ups less than David. How many push-ups did John do?
Zachary did 22 push-ups. 
David did 1 more push-up than Zachary, so he did 23. 
John did 20 push-ups less than David, so he did 3.