add gdp

README.md

@@ -27,3 +27,4 @@
 
 - [April 9 - Efficiency](apr9-efficiency.md)
 - [April 13 - Externalities](apr13-externality.md)
+- [April 18 - GDP](apr18-gdp.md)

apr18-gdp.md

@@ -0,0 +1,16 @@
+# April 18 - Gross Domestic Product
+
+A nation's **gross domestic product** (GDP) is the total dollar value of
+all final goods and services produced within the country's borders in a
+given year.
+
+- Dollar Value
+    - The **dollar price** is the measurement, not quantity
+
+- Goods and Services
+    - GDP includes both tangible goods and intanigble services
+
+- Final Products
+    - not products that become parts of other products
+
+- within a given year