A boat covers a certain distance downstream in 1 hour, while it comes back in 1½ hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?	Answers:	A) 12 kmph	B) 13 kmph	C) 14 kmph	D) 15 kmph	E) none

Rationale: sol . let the speed of the boat in still water be x kmph . then , speed downstream = ( x + 3 ) kmph , speed upstream = ( x - 3 ) kmph . ∴ ( x + 3 ) * 1 = ( x - 3 ) * 3 / 2 ⇔ 2 x + 6 = 3 x - 9 ⇔ x = 15 kmph . answer d
Answer: D