问题如下：
In a discrete uniform distribution with 20 potential outcomes of integers 1 to 20, the probability that X is greater than or equal to 3 but less than 6, P(3 ≤ X < 6), is:
选项：
A.0.10.
B.0.15.
C.0.20.
解释：
B is correct.
The probability of any outcome is 0.05, P(1) = 1/20 = 0.05. The probability that X is greater than or equal to 3 but less than 6, which is expressed as P(3 ≤ X < 6) = P(3) + P(4) + P(5) = 0.05 + 0.05 + 0.05 = 0.15
我的解题思路是连续均匀分布，（20-1）/x2-x1=20%;求出x2-x1=95；（6-3）/95=0.032。请问这个思路错在哪呢？
