diff --git a/mba-main.org b/mba-main.org
index 52f04fc..d686c2e 100644
--- a/mba-main.org
+++ b/mba-main.org
@@ -53,3 +53,7 @@
 #+attr_html: :class contents-overview
 - [[./mba/ch49.org][Chapter 49. How to Build Financial Statements for Private Companies the Easy Way]]
 - [[./mba/ch50.org][Chapter 50. How to value Private Companies + Growth Methods]]
+
+** Section 10 - Due Diligence and Data Sources
+#+attr_html: :class contents-overview
+- [[./mba/ch55.org][Chapter 55. Where to get Information for your Financial Model]]
diff --git a/mba/ch50.org b/mba/ch50.org
index 27ce15a..719f5bd 100644
--- a/mba/ch50.org
+++ b/mba/ch50.org
@@ -270,3 +270,41 @@ assuming the IPO takes place in 2020 our valuation will be
 *** retained earnings
 - part of equity
 - how much profit derived over the years
+
+** playing with equations
+
+*** go through the following equations
+1. \[\text{ROE (return on equity)} = \frac{\text{net income}}{\text{equity}} \]
+2.
+   \[\text{ROE (return on equity)} = \frac{\text{net income}}{\text{equity}} \times 1 \times 1 \]
+3.
+   \[\text{ROE (return on equity)} = \frac{\text{net income}}{\text{equity}} \times \frac{\text{sales}}{\text{sales}} \times \frac{\text{assets}}{\text{assets}} \]
+
+4.
+   \[\text{ROE (return on equity)} = \frac{\text{net income}}{\text{sales}} \times \frac{\text{sales}}{\text{assets}} \times \frac{\text{assets}}{\text{equity}} \]
+
+*** Lets break down this equation and define its parts
+**** first define ROE as Growth
+\[\text{Growth (ROE ie. return on equity)} = \frac{\text{net income}}{\text{sales}} \times \frac{\text{sales}}{\text{assets}} \times \frac{\text{assets}}{\text{equity}} \]
+
+**** now define the other parts of this equation
+   1. Net Profit Margin is Net Income over Sales
+      \[
+        \text{Net Profit Margin} = \frac{\text{net income}}{\text{sales}}
+      \]
+   2. Asset Turnover is Sales over Assets
+      \[
+        \text{Asset Turnover} = \frac{\text{sales}}{\text{assets}}
+      \]
+   3. Equity Multiplier is Asset over Equity
+      \[
+        \text{Equity Multiplier} = \frac{\text{assets}}{\text{equity}}
+      \]
+*** redefine the equation
+
+  \[\text{Growth} = \text{Net Profit Margin} \times \text{Asset Turnover} \times \text{Equity Multiplier} \]
+
+by increaseing one of the three parts of the equation you can increase growth
+1. Net Profit Margin
+2. Asset Turnover
+3. Equity Multiplier
diff --git a/mba/ch55.org b/mba/ch55.org
new file mode 100644
index 0000000..b6bd153
--- /dev/null
+++ b/mba/ch55.org
@@ -0,0 +1,8 @@
+#+title: Section 10 | Lesson 55 - Where to get Information for your Financial Models
+#+HTML_HEAD: <link rel="stylesheet" type="text/css" href="../_share/media/css/org-media-sass/categories/business.css" />
+
+* Links
+- [[./../mba-main.org][TOC | Business]]
+- [[https://www.udemy.com/course/an-entire-mba-in-1-courseaward-winning-business-school-prof/learn/lecture/4314666#overview][S10:L55. Where to get Information for your Financial Models]]
+
+* Notes