There is a little story about an insurance(保险) salesman in Tokyo. Even though this man tried very hard to promote the insurance, nobody bought it. One day, he came to a small temple and began to brag about his insurance. After listening to his introduction, the monk said: “Your recommendation of insurance can’t arouse any of my interests! When you are communicating with others, you must have the charm to attract others, or you will be unpromising in the future. Young man, try to change yourself!”
   The salesman thought deeply about each word. From then on, he invited all his friends to point out his weakness and kept on improving himself bit by bit for all his life. Thirty years later, he became a millionaire. And this man is the famous Yuan Yi Ping. His experience reflects one attitude: sometimes, we should change ourselves instead of changing the world.

在一个不透明的口袋中放入除颜色外其余都相同的6个红球和若干个绿球，小颖从中随机摸出一球，记下颜色后，放回，共试验60次，其中记有20个红球，估计袋中有绿球个数为（　　）

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