Question

A boat can row downstream 40 km in 2 hrs and upstream 8 km in 2 hrs. Find the speed of rowing in still water and the speed of the current.

Answer 1

Answer:

ɢɪᴠᴇɴ:-

★ A boat can row 40 km downstream in 2 hrs

& 8km upstream in 2 hrs

ᴛᴏ ғɪɴᴅ :-

★ The speed of rowing in still water

★ The speed of current

sᴏʟᴜᴛɪᴏɴ:-

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

& the speed of current be y km/hr

We know,

Time = Distance / Speed

Hence,

Speed downstream = (x+y) km/hr

&

speed upstream = (x-y) km/hr

Now,

40 / ( x+y) = 2

& 8/ (x-y) = 2

➱ x +y = 20........eq (1)

➱ x-y =4...... eq(2)

Adding both equations, we get

⇾ x +y = 20

⇾x -y = 4

____________

⇾2x = 24

➱ x = 12

Now, put the value of x in eq (1)

y = 8

Hence,

The speed of rowing in still water is = 12km/hr

& The speed of current is = 8 km/hr

${\huge{\mathcal{\tt{Hope \ It \ Helps..!!!}}}}$

Answer 2

Your Answer:

Given:-

• A boat can row downstream 40 km in 2 hrs
• Same boat can row upstream 8 km in 2 hrs

To Find:-

• Speed of boat in still water

Solution:-

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

and let the speed of current be y km/hr

Speed upstream = x - y

Speed downstream = x + y

In case 1

A boat can row 40km downstream in 2 hours

So, for downstream

• Distance = 40km
• Time = 2hours
• Speed = x + y

We know, speed = distance/time

So,

x + y = 40/2

=> x + y = 20 -----------(1)

In case 2

A boat can row 8km upstream in 2 hours

So, for downstream

• Distance = 8km
• Time = 2hours
• Speed = x - y

We know, speed = distance/time

So,

x - y = 8/2

=> x - y = 4 --------------(2)

Solving equation (1) and (2)

from equation 1, y = 20 -x ----------(3)

putting value of y from equation (3) to equation (2)

x - ( 20 - x ) = 4

=> x - 20 + x = 4

=> 2x = 24

=> x = 12

and

y = 8

So, the speed of rowing in still water is 12km/hr

and the speed of rowing in stream is 8km/hr