Xiao Minghua 100 yuan bought a bottle of coke and a bottle of coke 1 yuan, while the store held activities, and five bottles could be exchanged for one bottle of coke. Why did he drink 125 bottles of coke? 100+20+4 is obviously 124. Why drink 125 bottles?

Solution: The difficulty of this problem mainly lies in the last bottle. When there were four bottles left, Xiao mingcan asked the boss for a bottle of coke. After drinking it, he could have five bottles. He can return another bottle of coke to the boss.