A fill pipe can fill 1/2 of cistern in 30 minutes. In how many minutes, it can fill 1/2 of the cistern? Select the correct option:
A) 15 min	B) 20 min	C) 25 min	D) 30 min	E) 35 min

Rationale: "required time = 30 * 2 * 1 / 2 = 30 minutes answer is d"
Answer: D