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.

Problem: in what time will a train 50 m long cross an electric pole, it its speed be 360 km / hr ?
Options: a. 0.25, b. 0.5, c. 1.5, d. 2.5, e. 3.5
b

Problem: x does a work in 20 days. y does the same work in 40 days. in how many days they together will do the same work ?
Options: a. 10, b. 12, c. 20, d. 30, e. 13.33
e

Problem: each of the products produced yesterday was checked by worker x or worker y. 0.5 % of the products checked by worker x are defective and 0.8 % of the products checked by worker y are defective. if the total defective rate of all the products checked by worker x and worker y is 0.65 %, what fraction of the products was checked by worker y ?
Options: a. 1 / 5, b. 1 / 2, c. 2 / 3, d. 1 / 4, e. 2 / 5
b