diff --git a/02 Learning HTML5.md b/02 Learning HTML5.md
index 1f27f58..d9f610c 100644
--- a/02 Learning HTML5.md	
+++ b/02 Learning HTML5.md	
@@ -210,7 +210,7 @@ There are a couple of notable things about the `img` element:
 | src       | For locating the image file. The file path is normally given as relative path, starting from the directory where the HTML file is located.  |
 | alt       | For displaying an alternative text if the image cannot be displayed, or if the user prefers using a screen reader for accessibility purposes. |
 
-#### 3.3.1 Test Your Knowledge
+#### 3.3.1 Test Your Understanding
 
 1. Find photographs of the following computers and upload to the `images/` directory you created:
     1. Sinclair ZX Spectrum
@@ -231,7 +231,7 @@ Now we will learn how to embed audio in a website. There are a number of resourc
     2. Firefox needs an `.ogg` encoded version.
 3. You can also embed a [YouTube](https://www.youtube.com) video in an `<iframe>` or alternatively using the `<object>` element. This is achieved by clicking on the share button then on the **embed** link that is displayed. You copy the html code into your website.
 
-#### 3.4.1 Test Your Knowledge
+#### 3.4.1 Test Your Understanding
 
 1. Add the `guitar` audio file to the `index.html` web page. The file has been provided in the two required formats.
     1. Test that the audio plays in both Firefox and Chrome.
@@ -263,7 +263,7 @@ Verify that you understand the elements used in marking up the table:
 
 > A summary of all HTML table tags can be found [here](http://www.w3schools.com/html/html_tables.asp).
 
-### 4.1 Test your understanding
+### 4.1 Test your Understanding
 
 1. Modify the table structure to contain a column for Spectravideo home computer. Its data is: Spectravideo SV-328, Zilog Z80A CPU, 64kB RAM, 32kB ROM.
 2. Generate two additional rows where each row should have a multi-column cell (use `colspan` attribute):
diff --git a/04 Functions and Objects.md b/04 Functions and Objects.md
index 4faab1a..c069493 100644
--- a/04 Functions and Objects.md	
+++ b/04 Functions and Objects.md	
@@ -91,10 +91,11 @@ const sqr = num => num * num
 
 ### 1.2.1 Test Your Understanding
 
-//TODO: add an exercise on function expressions.
-
 1. Refactor the `remainder2` function expression to take advantage of the implicit return (you will need to reduce it to a single line of code).
 2. Compare this to the original version: which is more _readable_?
+3. Create a function expression that takes two string parameters and returns the longest string and assign this to a constant called `longest. check this works correctly.
+4. Modify the function expression so that it can handle any number of string parameters (use a _rest parameter_).
+5. Can you reduce this function expression to a single line (hint: explore using the [reduce function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce) combined with the [ternary operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator))?
 
 ### 1.3 Callbacks