Question

A motor boat covers a certain distance downstream in a river in 3 hours. it covers the same distance upstream in 3 and half an hour. if the speed of the water is 1.5 ikm/hr then the speed of the boat in still water is

Answer 1

S=3*(v+1.5)=3.5(v-1.5)
6v+9=7v-10.5
V=19.5

Answer 2

Let the speed of the boat in still water be x km/hr.

Then,

• The speed of the boat downstream = ( x + 1.5 )
• The speed of the boat upstream = ( x - 1.5 )

In Downstream

• Time = 3 hours

We know that,

Distance = Speed × Time

= ( x + 1.5 ) × 3

= (3x + 4.5) km

In Upstream

• Time = 3* 1/2= 7/2

We know that,

Distance = Speed × Time

= ( x - 1.5 ) × 7/2

= 7x/2 - 10.5/2

= 7x - 10.5 / 2

According to question:-

3x + 4.5 = 7x - 10.5/2

⇒ 2(3x + 4.5 ) = 7x - 10.5

⇒ 6x + 9.0 = 7x - 10.5

⇒ 6x - 7x = - 10.5 - 9.0

⇒ -x = -19.5

⇒ x = 19.5

∴ Speed of the boat = x = 19.5 km/hr.