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.

[EX Q]: Problem: in a certain pond, 50 fish were caught, tagged, and returned to the pond. a few days later, 50 fish were caught again, of which 5 were found to have been tagged. if the percent of tagged fish in the second catch approximates the percent of tagged fish in the pond, what is the approximate number of fish in the pond ?
Options: a. 400, b. 500, c. 1,250, d. 2,500, e. 10,000
[EX A]: b

[EX Q]: Problem: two taps a and b can fill a cistern in 12 minutes and 18 minutes respectively. they are turned on at the same time. if the tap a is turned off after 4 minutes, how long will tap b take to fill the rest of the cistern ?
Options: a. 8 min., b. 9 min., c. 10 min., d. 7 min., e. none of these
[EX A]: a

[EX Q]: Problem: what is the value of 100 p 2 ?
Options: a. 9801, b. 12000, c. 5600, d. 9900, e. none of these
[EX A]:
d