若将抽取出来的50名学生中成绩落在第四、第五组的学生组成一个培训小组，再从这个培训小组中随机挑选2名学生参加决赛．用列表法或画树状图法求：挑选的2名学生的初赛成绩恰好都在90分以上的概率．
题目分析：依题得第四组的频数是2，第五组的频数也是2，设第四的2名学生分别为
、
第五组的2名学生分别为
、
，列表(或画树状图)如下，
| A1 | A2 | B1 | B2 | |
| A1 | ―― | A1、A2 | A1、B1 | A1、B2 |
| A2 | A2、A1 | ―― | A2、B1 | A2、B2 |
| B1 | B1、A1 | B1、A2 | ―― | B1、B2 |
| B2 | B2、A1 | B2、A2 | B2、B1 | ―― |
由上表可知共有12种结果，其中两个都是90分以上的有两种结果，所以恰好都是在90分以上的概率为
点评：本题考查概率的知识，分析清楚各种情况，运用概率知识求解，本题属基础题，概率是中考必考内容，但都比较简单
| Every summer, Jean Piaget retreats to his cabin in the Alps, where he spends most of his days analyzing the mass of research data generated over the past year at his Center for Genetic Epistemology. During long walks along the mountain trails, he mulls over the latest experimental results, and in the cool mountain evenings, he formulates his conclusions. With the approach of fall, he will descend from the mountain, manuscript for a book and several journal articles in hand. This time-honored procedure of careful observation followed by seclusion for thought and synthesis, has enabled him to become the most prolific, if not the most famous psychologist of the century. Piaget has only been widely known in this country since the 1960s, when his works were translated from their original French. But he has been recognized as an expert in the field of cognitive development in Europe since the 1930s. In fact, Piaget’s publishing career can be traced to the year 1906, when as a child of ten, he published his careful notes on the habits of an albino sparrow he observed near his home in Switzerland. After his precocious debut as an ornithologist, he took an after school job at the local natural history museum, soon becoming an expert on mollusks. At the age of sixteen he was recommended for a curator’s position at the natural history museum in Geneva, but declined in favor of continuing his education. He studied natural science at the University of Neuchatel, obtaining his doctorate at the age of twenty-one. His readings in philosophy stimulated an intense interest in epistemology-the study of humans acquire knowledge. Convinced that cognitive development had a genetic basis. Piaget decided that the best way to approach epistemology would be through its behavioral and biological components. Psychology appeared to be the discipline that best incorporated this approach. |
The data Piaget was analyzing in his cabin in the Alps was mostly concerning
A．his findings of the wild life in the mountains.
B．his experiments on the plants and wild life in the mountains.
C．his past experiments on how human beings obtain their knowledge.
D．his working experience at his Center.