Question

A race-boat covers a distance of 60 km downstream in one and a half hour. It covers this distance upstream in 2 hours.The speed of the race-boat in still water is 35 km/hr. Find the speed of the stream.​

Answer 1

Answer:

And the upstream (U.S)speed = speed of race-boat– speed of stream. Now it is given that downstream speed is 60 km in one andhalf hours or we can say in 1.5 hour. ⇒D. S=601.5=40Km/hr.

Answer 2

Question:-

A race-boat covers a distance of 60 km downstream in one and a half hour. It covers this distance upstream in 2 hours.The speed of the race-boat in still water is 35 km/hr. Find the speed of the stream.

Required Answer:-

Given:-

• Covers a distance of 60km downstream in 1 and 1/2 hour
• Covers the distance in upstream in 2 hours
• Speed of the boat in still water is 35 km/hr

To Find:-

• The speed of the stream

Solution:-

Let,

• The speed of the boat in still water be x
• The speed of the stream be y

Therefore,

• Speed of downstream (D.S.)= Speed of race-boat + speed of stream

$\\ \sf{ \implies{(D.S.) = \bold{x + y} \: km/hr}} - - - - - - - - - - (1)$

And,

• Speed of upstream (U.S.)= Speed of race-boat - speed of stream

$\\ \sf{ \implies{(U.S.) = \bold{x - y} \: km/hr}} - - - - - - - - - - (2)$

Again, we know that:-

$\\ \underline{ \boxed{ \rm{Speed = \dfrac{Distance}{Time}}}}$

As we were given,

• Downstream speed is 60km/hr in 1 and 1/2 hour or 1.5 hour

$\\ \sf{ \therefore{D.S.= \dfrac{60}{1.5} \: km/hr = \bold{40km/hr}}}$

And,

• Upstream speed is 60km/hr in 2 hours

$\\ \sf{ \therefore{U.S.= \dfrac{60}{2} \: km/hr = \bold{30km/hr}}}$

From equation (1) and (2) we get,

$\\ \sf{ \implies{x + y = 40 - - - - - - - - - - (3)}}$

And,

$\\ \sf{ \implies{x - y = 30 - - - - - - - - - - (4)}}$

Now, adding equation (3) and (4) =>

$\\ \sf{ \implies{x + y + x - y = 40 + 30}}$

$\\ \sf{ \implies{2x = 70}}$

$\\ \sf{ \implies{x = \dfrac{70}{2}}}$

$\\ \sf{ \implies{ x = \bold{35}}}$

Now, substituting the value in equation (3)=>

$\\ \sf{ \implies{35 + y = 40}}$

$\\ \sf{ \implies{y = 40 - 35}}$

$\\ \sf{ \therefore{y = \red{ \bold{5}}}}$

$\\ \underline{ \rm{Hence \: the \: speed \: of \: the \: stream \: is \:\bold{ \green{5km/hr}}}}$