A fill pipe can fill 1/2 of cistern in 15 minutes. In how many minutes, it can fill 1/2 of the cistern? Choose the correct option.
A) 1 min  B) 5 min  C) 10 min  D) 15 min  E) 20 min

Rationale: "required time = 15 * 2 * 1 / 2 = 15 minutes answer is d"
Answer: D