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 coin is tossed two times. What is the probability that there is at the least one tail?

 Option A: 3/4

 Option B: 31/37

 Option C: 31/18

 Option D: 31/10

 Option E: 31/19
[EX A]: Option A

[EX Q]: Question: The average age of students in section A of 100 students is 20 years and the average age of students in section B of 150 students is 30 years. Find the average age of students in both sections taken together?

 Option A: 26 years

 Option B: 30years

 Option C: 15years

 Option D: 25years

 Option E: 20years
[EX A]: Option A

[EX Q]: Question: How many seconds will a 500 m long train take to cross a man walking with a speed of 3 km/hr in the direction of the moving train if the speed of the train is 63 km/hr?

 Option A: 22

 Option B: 30

 Option C: 99

 Option D: 77

 Option E: 12
[EX A]:
Option B