On a river, Q is the mid-point between two points P and

On a river, Q is the mid-point between two points P and R on the same bank of the river. A boat can go from P to Q and back in 12 hours, and from P to R in 16 hours 40 minutes. How long would it take to go from R to P ?

Let PQ = QR = d km.
Let speed of boat in still water be p kmph. and speed of current be q kmph.
According to the question,

	d	+	d	= 12 ..........(i)
	p + q		p - q

and	2d	= 16	40
	p - q		60

⇒	2d	= 16	2	=	50	......(ii)
	p - q		3		3

By equation (i) × 2 – (ii),

⇒	2d	+	2d	-	2d	= 24 -	50
	p + q		p - q		p - q		3

⇒	2d	=	72 - 50	=	22	= 7	1	hours
	p + q		3		3		3

3	1	hrs
	3

6	2	hrs
	3

7	1	hrs
	3