2. 外语
  3. In a group of 80 students, 24 are taking physics, 40 are taking mathematics, and 20 are taking both physics and mathematics. If

In a group of 80 students, 24 are taking physics, 40 are taking mathematics, and 20 are taking both physics and mathematics. If

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问题 In a group of 80 students, 24 are taking physics, 40 are taking mathematics, and 20 are taking both physics and mathematics. If a student were’ randomly selected from all of the 80 students, what is the probability that the student selected are taking neither physics nor mathematics?
选项 A、0.20
B、0.25
C、0.45
D、0.55
E、0.60
答案C
解析 设集合A是注册物理的同学，集合B是注册数学的同学，那么A=24，B=40，AB=20，T=8，T=A+B-AB+N，代入后得到：80=24+40-20+N，N=36，即两门课都没有注册的人数为36，那么所求概率为36/80=0.45。
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