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.
--------
Question: Problem: a bag contains 10 green and 8 white balls. if two balls are drawn simultaneously, the probability that both are of the same colour is
Options: a. 8 / 15, b. 21 / 44, c. 3 / 5, d. 11 / 15, e. 7 / 15

Answer: b


Question: Problem: if a sum of money doubles itself in 20 years at simple interest, the ratepercent per annum is
Options: a. 12, b. 12.5, c. 13, d. 5, e. 14

Answer: d


Question: Problem: 9 men working 8 hours per day dig 30 m deep. how many extra men should be put to dig to a depth of 50 m working 6 hours per day ?
Options: a. 33, b. 66, c. 88, d. 11, e. 281

Answer:
d