START's reply

===> How many people live in Africa's fifth largest country?

I know that Africa's fifth largest country is Chad (source: The World Factbook).

Using this information, I determined how many people live in Chad:

Chad

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Population:
11,631,456 (July 2015 est.)

Age structure:
0-14 years: 44.2% (male 2,607,314/female 2,534,163)
15-24 years: 20.9% (male 1,183,962/female 1,247,130)
25-54 years: 28.05% (male 1,479,285/female 1,783,014)
55-64 years: 3.87% (male 197,673/female 252,379)
65 years and over: 2.98% (male 143,712/female 202,824) (2015 est.)

Source: The World Factbook