A person can row 71 km an hour in still water and

A person can row 7 1 km an hour in still water and he finds
2

that it takes him twice as long to row up as to row down the river. The speed of the stream is :

Let the speed of current be y kmph.
According to question ,

∴ 2		15	- y		=	15	+ y
		2				2

⇒ 15 - 2y =	15	+ y
	2

⇒ 3y = 15 -	15	=	15
	2		2

⇒ y =	5	= 2	1	kmph
	2		2

We can find the required answer with the help of given formula :

Here, Speed of Boat =	15	kmph
	2

t₁ = 2k, t₂ = k

	Speed of Boat	=	t₁ + t₂
	Speed of Stream		t₁ - t₂

		15		=	2k + k
		2 × Speed of Stream			2k - k

Speed of Stream = 2.5 km/hr