Zachary did 25 push-ups in gym class today. David did 10 more push-ups than Zachary. John did 13 push-ups less than david. How many push-ups did David do?
Zachary did 25 push-ups. 
David did 10 more than Zachary, so he did 35 push-ups. 
John did 13 less than David, so he did 22 push-ups.