A man rows a boat 18 kilometres in 4 hours downstream and

A man rows a boat 18 kilometres in 4 hours downstream and returns upstream in 12 hours. The speed of the stream (in km per hour) is :

From the given in question ,

Rate downstream =	18	=	9	kmph
	4		2

Rate upstream =	18	=	3	kmph
	12		2

Now, speed of the stream =	Rate downstream – Rate upstream
	2

speed of the stream =	6	=	3	= 1.5 kmph.
	4		2

Second method to solve this question :
Here, y = 18, t₁ = 4, t₂ = 12

Speed of stream =	y		1	-	1
	2		t₁		t₂

Speed of stream =	18		1	-	1
	2		4		12

Speed of stream = 9		3 - 1
		12

Hence , Speed of stream = 1.5 km/hr