一个盒子中装有4个编号依次为1、2、3、4的球，这4个球除号码外完全相同，先从盒子中随机取一个球，该球的编号为X，将球放回袋中，然后再从袋中随机取一个球，该球的编号为Y
（1）列出所有可能结果．
（2）求事件A=“取出球的号码之和小于4”的概率．
（3）求事件B=“编号X＜Y”的概率．
（1）所有可能的结果共有（1，1）、（1，2）、（1，3）、（1，4）、（2，1）、（2，2）、（2，3）、（2，4）、
（3，1）、（3，2）、（3，3）、（3，4）、（4，1）、（4，2）、（4，3）、（4，4），共计16个．
（2）事件“取出球的号码之和小于4”包含的结果有（1，1）、（1，2）、（2，1），共计3个，
故“取出球的号码之和小于4”的概率为
．3 16
（3）事件B=“编号X＜Y”包含的结果有 （1，2）、（1，3）、（1，4）、（2，3）、（2，4）、（3，4），共计6个，
故事件B=“编号X＜Y”的概率为
=6 16
．3 8
The story tell us about the British writer, Richard Savage. He was once living in London with 1 money in his pockets. In order to get some food and clothes, he wrote the story of his life and managed to have it published. But not many copies of his books were 2 in the shops, and he was still living a hard life. Because of anxiety(忧虑)and malnutrition(营养不良)， he became very weak and before long he fell 3 , and a doctor was sent for. The doctor was not rich enough, but was 4 literature. He tried his best to cure Savage of his illness and a week later Savage was out of danger. When he finally recovered(重新获得) his 5 , the doctor sent a bill to Savage for his 6 , but poor Savage had no money to pay it. The doctor waited for a month and sent another bill. Receiving no money again, the doctor went to Savage himself. "You know you owe(欠) your life to me," said the doctor, "and I should 7 some thankfulness from you." "I agree," said the writer, " you've done a great favour(恩惠) for me and if I'm not ungrateful for your kindness, I'll damage(损坏) my life to you." With these words he handed the doctor two copies of The Life of Richard Savage. The doctor took the books home and began to _ 8 them carefully. "I see I've 9 the life of a great writer," the doctor said to himself with a sense of pride, Maybe this is the only thing I could be really 10 of in my life." Five years later Savage called on the doctor to pay his bill, only to find that the doctor had already passed away .
|