某学校高二年级有12名语文教师、13名数学教师、15名英语教师,市教育局拟召开一个新课程研讨会.
(1)若选派1名教师参会,有多少种派法?
(2)若三个学科各派1名教师参会,有多少种派法?
(3)若选派2名不同学科的教师参会,有多少种派法?
⑴40，⑵2340，⑶531
(1)分三类:第一类选语文老师,有12种不同选法; 第二类选数学老师,有13种不同选法; 第三类选英语老师,有15种不同选法.共有12+13+15=40种不同的选法.
(2)分三步: 第一步选语文老师,有12种不同选法; 第二步选数学老师,有13种不同选法; 第三步选英语老师,有15种不同选法.共有12×13×15=2340种不同的选法.
(3)分三类:选一位语文老师和一位数学老师共有12×13种不同的选法;选一位语文老师和一位英语老师共有12×15种不同的选法;选一位英语老师和一位数学老师共有15×13种不同的选法.共有12×13+12×15+13×15=531种不同的选法.
When I was young, I liked to play jokes on people I knew, especially on my parents and friends. One day my mother was and I was playing with my younger brother Tony. Suddenly I ran to my mother and said, “Tony fell from the open window!” She was very and ran out of the kitchen. Then I said, “Don’t worry, I’m just .” And my mother shouted at me, “If you do it , I’ll hit you.” One day I went swimming with my in the sea. I wanted to play a joke on them. In the beginning, I went swimming , and I called out, “Help!” All my friends came to help me, only to find that I was joking. But the next time I wasn’t joking. I was so that I swam in deep water. I tried my test to call my friends for help, but this time came to help me. they found I was telling the truth. They came and saved my life. They took me to the hospital. This is the best in my life. From then on, I haven’t joked on anyone.
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