有五张卡片，它们的正、反面分别写0与1，2与3，4与5，6与7，8与9，将其中任意三张并排放在一起组成三位数，共可组成多少个不同的三位数？
432个
解法一(间接法): 任取三张卡片可以组成不同三位数C
·23·A
(个)，其中0在百位的有C
·22·A
(个)，这是不合题意的，故共有不同三位数
C·23·A－C·22·A=432(个）.
解法二 (直接法) : 第一类： 0与1卡片放首位，可以组成不同三位数有
(个); 第二类： 0与1卡片不放首位，可以组成不同三位数有
(个).
故共有不同三位数 48+384＝432(个）.
| 阅读理解。 | ||||||||||||||||||||||||||||||||||||||||||||
| The following table shows some results of a survey. 800 Japanese students were asked to tell what they thought of their teachers. There are three kinds of teachers: the new (with less than three years' teaching), the middle-aged (ten to twenty years), and the old (twenty to thirty years). The numbers in the table show the percentage (百分率) of the students who answered "very satisfied (满意) for each question item."
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| 1. The old teachers are loved by most of the students in their ability (能力) to ___________. | ||||||||||||||||||||||||||||||||||||||||||||
[ ] | ||||||||||||||||||||||||||||||||||||||||||||
| A. be fair to any students B. listen to what students say C. explain texts clearly D. understand and play with students | ||||||||||||||||||||||||||||||||||||||||||||
| 2. What kind of teachers'lessons are the most interesting? | ||||||||||||||||||||||||||||||||||||||||||||
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| A. The new. B. The middle-aged. C. The old. D. We don't know. | ||||||||||||||||||||||||||||||||||||||||||||
| 3. According to the table, which of the following is true? | ||||||||||||||||||||||||||||||||||||||||||||
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| A. In the new teachers'classes, students seem to ask questions more freely. B. Many students seem to be satisfied with the new teachers'handwriting. C. The middle-aged teachers spend the most time with students after class. D. After class, the new teachers like to stay with students more often. |