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 Input:
Problem: a bottle contains a certain solution. in the bottled solution, the ratio of water to soap is 3: 4, and the ratio of soap to salt is five times this ratio. the solution is poured into an open container, and after some time, the ratio of water to soap in the open container is halved by water evaporation. at that time, what is the ratio of water to salt in the solution ?
Options: a. 9: 32, b. 9: 30, c. 32: 9, d. 19: 32, e. 18: 30

Ex Output:
a


Ex Input:
Problem: the arithmetic mean and standard deviation of a certain normal distribution are 14.5 and 1.7, respectively. what value is exactly 2 standard deviations less than the mean ?
Options: a. 10.5, b. 11, c. 11.1, d. 12, e. 12.5

Ex Output:
c


Ex Input:
Problem: calculate the amount that an investor needs to be invest to earn $ 1005 in interest in 12 months if the investor plans to invest x dollars in a savings account that pays interest at an annual rate of 11 % compounded semi - annually ?
Options: a. 8000, b. 8100, c. 8900, d. 8600, e. 8400

Ex Output:

c