added part 4 - building algorithms

.gitignore

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+.DS_Store

README.md

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 As much as this series is created to help educate aspiring computer programmers and data scientists of all ages with no previous programming experience, after playing with computers and numbers for nearly 4 decades, I've also made this as a reminder for myself on how to have fun with computers and maths.
 
-Using Jupyter notebooks as the medium, this series provides an introduction to: 
+Using Jupyter notebooks as an interactive learning medium, this series provides an introduction to:
 
 - Computer Science
 - Python programming language
-- Numerical computing 
-- Numbers theory 
-- Prime numbers 
+- Numerical computing
+- Numbers theory
+- Prime numbers
 - Data visualization
 - Deep learning
 
-#### Launch in Azure (requires logging in): 
+#### Interactive in Mybinder:
+
+[![Binder](https://mybinder.org/badge.svg)](https://mybinder.org/v2/gh/mikkokotila/jupyter4kids/master?filepath=notebooks)
+
+#### Interative in Azure (requires logging in):
 
 <a href="https://notebooks.azure.com/import/gh/mikkokotila/jupyter4kids"><img src="https://notebooks.azure.com/launch.png" /></a>
 
+#### Static in Nbviewer:
+
+Use the link provided for each part below the corresponding title.
+
 ## Part 1 : Introduction
 
 Start learning [here](https://nbviewer.jupyter.org/github/mikkokotila/jupyter4kids/blob/master/notebooks/numerical-computing-is-fun-1.ipynb).
 
-What you will learn: 
+What you will learn:
 
 - print() is the command to print something on the screen
 - Math operations are very easy to perform in Python
@@ -35,7 +43,7 @@ What you will learn:
 
 Continue learning [here](https://nbviewer.jupyter.org/github/mikkokotila/jupyter4kids/blob/master/notebooks/numerical-computing-is-fun-2.ipynb)
 
-What you will learn: 
+What you will learn:
 
 - Prime numbers relate with divisibility
 - Divisibility means that when one number is divided by other, the product is not a whole number
@@ -50,19 +58,37 @@ What you will learn:
 - The biggest prime number is a really big number
 - Very big numbers require vast networks of computers joined together
 
-## Part 3 : Algorithms 
+## Part 3 : Algorithms Overview
 
 Continue learning [here](https://nbviewer.jupyter.org/github/mikkokotila/jupyter4kids/blob/master/notebooks/numerical-computing-is-fun-3.ipynb).
 
-What you will learn: 
+What you will learn:
 
 - Algorithms are like insides of factories
 - Algorithms take inputs and give outputs
 - Conditional statements are a tool for putting boolean logic in to action
 - The three conditional statements in Python are 'if', 'else' and 'elif'
 - Even just 'if' alone can be used to create a conditional statement
 - With small changes to our code, we can make big improvements in capability
-- It's very convinient to store values in to memory
+- It's very convenient to store values in to memory
 - Computer memory is nothing like human memory, and also not like a safe deposit box
 - Any value can be stored in to memory
 - Numbers can be automatically generated with range() function
+
+## Part 4: Building Algorithms
+
+Continue learning [here](https://nbviewer.jupyter.org/github/mikkokotila/jupyter4kids/blob/master/notebooks/numerical-computing-is-fun-4.ipynb).
+
+What you will learn: 
+
+- Problems tend to have two sides; easy and hard
+- It's easy to find non-primes, but hard to find primes 
+- Computers can't think at all, they just process commands
+- The better the rules, the better the job the computer can do
+- Performance of the program matters (sometimes a lot)
+- Make small changes, get big gains
+- Timing how fast computer programs run
+- More boolean operators 
+- Finding and dealing with bugs in your code
+- When to let bugs just be
+- Numbers theory is a great way to have fun with numbers!