2. 外语
  3. In a series of races, 10 toy cars are raced, 2 cars at a time. If each car must race each of the other cars exactly twice, how

In a series of races, 10 toy cars are raced, 2 cars at a time. If each car must race each of the other cars exactly twice, how

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问题 In a series of races, 10 toy cars are raced, 2 cars at a time. If each car must race each of the other cars  exactly twice, how many races must be held?
选项 A、40
B、90
C、100
D、180
E、200
答案B
解析 在一系列比赛中，有10辆玩具汽车进行比赛，每场比赛有2辆汽车参加。若每辆汽车必须和其他的各辆汽车比赛两次，问一共要举行有多少场比赛?
解：本题的正确答案为(B)。10辆车中，每辆车与另一辆车比赛一次，相当于从10辆汽车中任选2辆车比赛，共45次；而比赛2次，则共有2×45=90次。
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