diff --git a/education/statistics/random-variable.md b/education/statistics/random-variable.md
index 0eff42c..9212555 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: 2025-12-28T17:02:16.122Z
+date: 2025-12-28T17:09:49.339Z
 tags: 
 editor: markdown
 dateCreated: 2025-12-28T16:41:51.938Z
@@ -27,5 +27,12 @@ $F(X) = \sum_{y : y \leq x} P(X = y)$
 ## Continuous
 
 ### Probability Density Function (PDF)
+Probabilistic properties of a continuous random variable.
+
+$\int f(x) \,dx\ = 1$
+
+### Cumulative Distribution Function (CDF)
+
+$F(X) = P(X \leq x) = \int_{-\infty}^{x} f(y) \,dy\\$
+
 
-### Cumulative Distribution Function (CDF)
\ No newline at end of file