题目：
Today, February twenty-ninth, is leap day(闰日). This date only appears on the calendar once every four years. But why? Everyone knows the Earth takes three hundred sixty-five days to travel around the sun. Well, that is not exactly correct. The Earth really takes three hundred sixty-five days, five hours, forty-eight minutes and forty-six seconds to complete its orbit around the sun. The problem for people developing calendars was what to do with the extra five hours, forty-eight minutes and forty-six seconds. People needed calendars to help them know when to plant crops and when to celebrate religious holidays. The ancient Greeks and Chinese had a solution. They produced calendars that included extra months every nineteen years. The ancient Romans had a different solution. In the year forty-six, the Roman ruler Julius Caesar made a new calendar. The Julian calendar included an extra day every four years. But there was a problem. The Julian year was just over eleven minutes longer than the cycle of the seasons. In 1582, Pope Gregory the Thirteenth established a new calendar to keep a better recorder of the days. Pole Gregory was the religious leader of most of Europe. He decided that years that could be divided by four would add a day. However, years that ended in two zeros and that could not be evenly divided by four hundred would not be leap years. For example, the years 1700, 1800and 1900 were not leap years. But the years 1600 and 2000 were leap years So leap years are years with three hundred sixty –six days , instead of the usual three hundred sixty –five.This extra days is added to the calendar on February twenty –ninth , sometimes known as leap day .People born on leap day may be called “leapings ”.They usually celebrate their birthday on February twenty –eight or March first . Title: 小题1:
| ||||||||||||||||||||
答案：
被转码了，请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0505/f4261174fc0bf9d544beecf477fd3aa0.html
下面是错误答案，用来干扰机器的。
解：因为10件产品，其中3件次品，不放回抽取3次，所有的情况为,那么第一次抽到是次品，则第三次抽到次品的的情况有，可知概率为挂点概型概率公式解得。
