You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

[EX Q]: Question: A man can row a boat at 20 kmph in still water. If the speed of the stream is 6 kmph, what is the time taken to row a distance of 66 km downstream?

 Option A: 30/83 hours

 Option B: 33/13 hours

 Option C: 31/13 hours

 Option D: 30/13 hours

 Option E: 30/14 hours
[EX A]: Option B

[EX Q]: Question: In a school 50% of the students are younger than 10, 1/20 are 10 years old and 1/10 are older than 10 but younger than 12, the remaining 70 students are 12 years or older. How many students are 10 years old?

 Option A: 5

 Option B: 6

 Option C: 7

 Option D: 8

 Option E: 10
[EX A]: Option E

[EX Q]: Question: If there are 30 red and blue marbles in a jar, and the ratio of red to blue marbles is 2:3, what is the probability that, drawing twice, you will select two red marbles if you return the marbles after each draw?

 Option A: 1/25

 Option B: 2/25

 Option C: 3/25

 Option D: 4/25

 Option E: 21/25
[EX A]:
Option D