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：
A.
0.20.
B.
0.35.
C.
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.
如题。。。。。。。。
