premise: Baghdad (Arabic: بغداد‎ ‎ , ) is the capital of Iraq. The population of Baghdad, as of 2016 , is approximately 8,765,000, making it the largest city in Iraq, the second largest city in the Arab world (after Cairo, Egypt), and the second largest city in Western Asia (after Tehran, Iran).
hypothesis: Tehran has a larger population than Cairo.
reason: From the text we know that Cairo is the largest city in the Arab world and Tehran is the largest city in Western Asia but have been given no information about which of those two would be larger (I had to look it up- it is actually Cairo)