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.

[Q]: Problem: a train covers a distance of 100 km in 1 hour. if its speed is decreased by 15 km / hr, the time taken by the car to cover the same distance will be ?
Options: a. 1 hr, b. 1 hr 10 min, c. 50 min, d. 1 hr 30 min, e. 1 hr 45 min
[A]: b


[Q]: Problem: two trains of equal length are running on parallel lines in the same directions at 46 km / hr. and 36 km / hr. the faster trains pass the slower train in 72 seconds. the length of each train is :
Options: a. 82 m, b. 50 m, c. 72 m, d. 100 m, e. none of these
[A]: d


[Q]: Problem: ifaequals the sum of the even integers from 2 to 20, inclusive, andbequals the sum of the odd integers from 1 to 19, inclusive, what is the value of a * b ?
Options: a. 10000, b. 11000, c. 19000, d. 20000, e. 21000
[A]:
b