The easiest way of determining the number of U.S troops in Iraq is:
98 thousand troops (2010) - 23 thousand = 75 thousand troops (half)
What's left to do is multiply 75 thousand by 2, and you get the number of U.S troops in Iraq.
75 thousand x 2 = 150 thousand troops.
There were a total of 150 thousand US troops in Iraq in 2003