What is the total population of the Middle East?
Depends on what countries you count as being in the Middle East. Go to http://www.cia.gov/cia/publications/factbook/rankorder/2119rank.html and add up the populations of every country you count, and there you go.
Depends how you define “Middle East”, which has a variable definition. If we call the ME the region from Egypt to Iran, including both those states as well as Turkey, but excluding the former Soviet republics of the Caucasus, it’s maybe ~300-325 million. The big three in that grouping would be Egypt, Turkey, and Iran.