The mongols developed a nomadic society in their central asian homeland with an economy based on

The best answer would probably be trade when considering the duration of their whole empire. 

However, a good portion of the starting capital Mongols had was received by looting and ransacking cities. The Mongols were actually notorious for ransacking cities and taking everything that was valuable, also killing the local population. 

They did, on the other hand, also establish trade with different neighbouring nations which allowed them to gain additional streams of revenue. 

1920 census

the census was scheduled for january the 1st, as the government believed that more farmers would be in their homes by that time instead of april. the census did not ask about unemployment, the number of children, and how long was a couple married were not taken into consideration. individuals were considered as residents of the places they normally slept, not the places were they worked at or visited.

2010 census

the census was scheduled for april 1st, 2010. it was the shortest census in history: it only contained 10 questions related to name, age, gender, ethnicity, relationship, and whether the citizen owned a home or rented one. the government launched a website in order to provide the citizens with information regarding the census. there were also "teach census weeks" in schools nationwide.