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: cereal a is 10 % sugar by weight, whereas healthier but less delicious cereal b is 2 % sugar by weight. to make a delicious and healthy mixture that is 3 % sugar, what should be the ratio of cereal a to cereal b, by weight ?
Options: a. 2: 9, b. 2: 7, c. 1: 7, d. 1: 4, e. 1: 3
[EX A]: c

[EX Q]: Problem: if n = 2 ^ 0.15 and n ^ b = 1, b must equal
Options: a. 3 / 80, b. 20 / 3, c. 4, d. 5 / 3, e. 80 / 3
[EX A]: b

[EX Q]: Problem: if 25 % of a number is equal to one - third of another number, what is the ratio of first number to the second number ?
Options: a. 4: 3, b. 1: 4, c. 3: 7, d. 6: 11, e. 2: 3
[EX A]:
a