A joke about saving money

Xiaohong is a playful child and loves to spend money. She always fails in her lessons, and she always spends more money than other children. In order to make her spend less money, her mother repeatedly taught her to save every penny. But in order to let her pass the exam, her mother promised to give her 10 yuan a reward for passing the exam.

One day, Xiaohong asked her mother, "You won't be angry if I deposit 10 yuan for you, will you?"

Mom was very happy to hear that. She touched Xiaohong's head and said, "Of course not, so mom will be happier. Tell mom, how did you save me 10 yuan? "

Xiaohong suddenly took out his paper and said, "I failed the exam again, so 10 yuan's reward is for you!" " "