more progress!

study/001_introduction-to-probability-statistics-and-random-processes/README.md

@@ -2,4 +2,10 @@
 
 total pages=1007
 
-**Currently reading:** chapter 1, page 153
+**Currently reading:** chapter 3, page 157
+
+TODO:
+
+- ch1 end of chapter problems
+- ch2 end of chapter problems
+- ch3 end of chapter problems

study/001_introduction-to-probability-statistics-and-random-processes/ch3/notes.ipynb

@@ -31,7 +31,13 @@
    "id": "9f0046c2",
    "metadata": {},
    "source": [
-    "## Discrete Random Variables (3.1.1 - 3.1.2)"
+    "## Random Variables (3.1.1 - 3.1.2)\n",
+    "\n",
+    "***Definition.*** Random Variables: \\\n",
+    "A random variable $X$ is a function from the sample space to the real numbers. ie\n",
+    "$$X : S \\to \\mathbb{R}$$\n",
+    "\n",
+    "***Definition.*** $X$ is a discrete random variable, if its range is countable\n"
    ]
   }
  ],