请问为什么F（4）-F（3）=p4呢？
谢谢
问题如下图：
选项：
A. 
B. 
C. 
解释：
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
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. 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
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。。。。。。。。
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？
老师，这道题的表格 看不懂是什么意思，麻烦解答，谢谢！
