A salt manufacturing company produced a total of 1000 tonnes of salt in January of a particular year. Starting from February its production increased by 100 tonnes every month over the previous months until the end of the year. Find its average monthly production for that year? Choose the correct choice from the following choices
A) 1750
B) 2789
C) 2500
D) 1550
E) 2000

Rationale: total production of salt by the company in that year = 1000 + 1100 + 1200 + . . . . + 2100 = 18600 . average monthly production of salt for that year = 18600 / 12 = 1550 . answer : d
Answer: D