A boat running downstream covers a distance of 20km in 2

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A boat running downstream covers a distance of 20km in 2 hrs while it covers the same distance upstream in 5 hrs. Then speed of the boat in still water is

1. 7 km/hr
2. 8 km/hr
3. 9 km/hr
4. 10 km/hr

Correct Option: A

Let the speed of boat in still water be p kmph and that of stream be q kmph.

∴	20	= 2
	p + q

⇒ p + q = 10 ...(i)

	20	= 5
	p - q

⇒ p – q = 4 ...(ii)
On adding, 2p = 14 kmph ⇒ p = 7 kmph
We can find the required answer with the help of given formula :
Here, y = 20, t₁ = 2, t₂ = 5

Speed of Boat =	y		1	+	1
	2		t₁		t₂

Speed of Boat =	20		1	+	1		= 7 km/hr
	2		2		5