There are 20 hands in Peter's class, not including his. Assume every student in the class has 2 arms and 2 hands. How many students are in Peter's class including him? Let's answer step by step:
There are 20 + 2 of Peter's hands = 22 hands in Peter's class including his. There are 22 hands / 2 hands per student = 11 students. The answer: 11.