diff --git a/education/statistics/random-variable.md b/education/statistics/random-variable.md
index 7257eb3..0eff42c 100644
--- a/education/statistics/random-variable.md
+++ b/education/statistics/random-variable.md
@@ -2,7 +2,7 @@
 title: 隨機變數 (Random Variable)
 description: 
 published: true
-date: 2025-12-28T16:58:42.847Z
+date: 2025-12-28T17:02:16.122Z
 tags: 
 editor: markdown
 dateCreated: 2025-12-28T16:41:51.938Z
@@ -17,10 +17,13 @@ A set of probability value **p~i~** assigned to each of the values taken by the
 $0 \leq p_i \leq 1$ and $\sum_{p_i} = 1$
 
 Probability
-$P(X=x)=p_i$
+$P(X = x) = p_i$
 
 ### Cumulative Distribution Function (CDF)
 
+$F(X) = P(X \leq x)$
+$F(X) = \sum_{y : y \leq x} P(X = y)$
+
 ## Continuous
 
 ### Probability Density Function (PDF)