Static Typing Vs Dynamic Typing

Recently I have been reading an article published by partners of internet.org. In the article its been mentioned that using PHP (a dynamic typed language) was very productive for Facebook. I tried understanding why is using dynamic typed languages productive and went through some readings. I am sharing a few which were a good read.

1. http://programmers.stackexchange.com/questions/10032/dynamically-vs-statically-typed-languages-studies

2. http://programmers.stackexchange.com/questions/122205/what-is-the-supposed-productivity-gain-of-dynamic-typing

3. http://www.sitepoint.com/typing-versus-dynamic-typing/

You can find many other resources but the above ones should give a quick overview of typing. Wiki articles are also a good place to start learning.

PS : I would strongly recommend people to read the article that is published from internet.org.