p（A or B）=Pa+Pb

NO.PZ2017092702000091

问题如下：

The cumulative distribution function for a discrete random variable is shown in the following table.

The probability that X will take on a value of either 2 or 4 is closest to:

选项：

0.20.

0.35.

0.85.

解释：

A is correct.

The probability that X will take on a value of 4 or less is: F(4) = P(X ≤ 4) = p(1) + p(2) + p(3) + p(4) = 0.60. The probability that X will take on a value of 3 or less is: F(3) = P(X ≤ 3) = p(1) + p(2) + p(3) = 0.50. So, the probability that X will take on a value of 4 is: F(4) – F(3) = p(4) = 0.10. The probability of X = 2 can be found using the same logic: F(2) – F(1) = p(2) = 0.25 – 0.15 = 0.10. The probability of X taking on a value of 2 or 4 is: p(2) + p(4) = 0.10 + 0.10 = 0.20.

老师这道题里为什么要求x小于等于4的概率和x小于等于2的概率，直接用x=4和2的概率相加不行吗

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星星_品职助教 · 2023年03月16日

同学你好，

求“x小于等于4的概率和x小于等于2的概率”的目的就是要“用x=4和2的概率相加”。

表格中给出的是F(x)，也就是累积概率函数，F(4)的意思是所有小于等于4的概率之和，并不是X=4的概率。只有通过F(4) – F(3)，才能得到X=4的概率，也就是p(4)。

同理，只有通过F(2) – F(1)，才能得到X=2的概率，也就是p(2) 。

此后用p(2) + p(4) ，也就是“直接用x=4和2的概率相加”。

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NO.PZ2017092702000091 问题如下 The cumulative stribution function for a screte ranm variable is shown in the following table. The probability thX will take on a value of either 2 or 4 is closest to: A.0.20. B.0.35. C.0.85. A is correct. The probability thX will take on a value of 4 or less is: F(4) = P(X ≤ 4) = p(1) + p(2) + p(3) + p(4) = 0.60. The probability thX will take on a value of 3 or less is: F(3) = P(X ≤ 3) = p(1) + p(2) + p(3) = 0.50. So, the probability thX will take on a value of 4 is: F(4) – F(3) = p(4) = 0.10. The probability of X = 2 cfounusing the same logiF(2) – F(1) = p(2) = 0.25 – 0.15 = 0.10. The probability of X taking on a value of 2 or 4 is: p(2) + p(4) = 0.10 + 0.10 = 0.20. 为什么不是0.1+0.1-0.01=0.19

2023-06-16 17:00 2 · 回答

NO.PZ2017092702000091问题如下The cumulative stribution function for a screte ranm variable is shown in the following table. The probability thX will take on a value of either 2 or 4 is closest to:A.0.20.B.0.35.C.0.85.A is correct. The probability thX will take on a value of 4 or less is: F(4) = P(X ≤ 4) = p(1) + p(2) + p(3) + p(4) = 0.60. The probability thX will take on a value of 3 or less is: F(3) = P(X ≤ 3) = p(1) + p(2) + p(3) = 0.50. So, the probability thX will take on a value of 4 is: F(4) – F(3) = p(4) = 0.10. The probability of X = 2 cfounusing the same logiF(2) – F(1) = p(2) = 0.25 – 0.15 = 0.10. The probability of X taking on a value of 2 or 4 is: p(2) + p(4) = 0.10 + 0.10 = 0.20.如题。。。。。。。。

2023-02-06 13:42 1 · 回答

The probability that X will take on a value of either 2 or 4 is closest to 是同时取2和4的概率的意思？

2020-06-01 20:15 1 · 回答

老师，这道题的表格看不懂是什么意思，麻烦解答，谢谢！

2019-09-12 19:35 1 · 回答

p（A or B）=Pa+Pb

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