1. Petya was exchanging stickers. He trades one sticker for 5 others. At first, he had 1 sticker. How many stickers will he have after 50 exchanges?
Answer: 201.

Solution: After each exchange, the number of Petya's stickers increases by 4 (one sticker disappears and 5 new ones appear). After 50 exchanges, the number of stickers will increase by 50*4=200. Initially, Petya had one sticker, so after 50 exchanges, he will have $1+200=201$.