Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

[EX Q]: Problem: a and b invests rs. 2500 and rs. 4000 respectively in a business. if a doubles his capital after 6 months. in what ratio should a and b divide that year ' s profit ?
Options: a. 11: 5, b. 15: 16, c. 15: 2, d. 9: 9, e. 11: 1
[EX A]: b

[EX Q]: Problem: what is the sum of natural numbers between 30 and 100
Options: a. 4615, b. 4860, c. 5000, d. 5500, e. 5550
[EX A]: a

[EX Q]: Problem: a train running at the speed of 100 km / hr crosses a pole in 9 sec. what is the length of the train ?
Options: a. 298 m, b. 250 m, c. 208 m, d. 988 m, e. 299 m
[EX A]:
b