if 2 pipes take an hour to fill a tank, then how long should 8 pipes take to fill the same tank?
Options:	A) 20 min	B) 10 min	C) 15 min	D) 25 min	E) 30 min

Rationale: if 2 pipes take an hour to fill a tank , then 8 pipes will take 2 * 60 / 8 = 15 mins to dig a ditch of the same type . answer : c
Answer: C