Question

On a bright Sunday morning three friends A, B and C decided to go for fishing and

boating. They decided to leave for the place together in the evening. The journey

was smooth, it just went as scheduled then they reached to the river, and started to set the boat on sail. They were enjoying their ride with full speed. They started

boating from a place to another place which is at a distance of 42 km and then

again returns to the starting place. They took 20 hours in all. The time taken by

them riding 14km downstream is equal to the time taken by them riding 6 km

upstream.



Plz Solve all MCQs​

Answer 1

Given :   boating from a place to another place which is at a distance of 42 km and then again returns to the starting place. They took 20 hours in all. The time taken by them riding 14km downstream is equal to the time taken by them riding 6 km upstream

To Find :  Boat speed in still water

River speed

Upstream speed

If speed of boat in still water increased by 1 and river speed decreased by 1 then time for return journey

Solution:

D = 42 km

Speed in still water  = B km/hr

Speed of stream / river   = S km/hr

Upstream speed =  B - S km/hr

Down stream speed =  B + S  km/hr

They took 20 hours in all

=> 42/(B - S)  + 42/(B + S)  = 20

=> 42( 2B )  = 20 ( B + S)(B - S)

=> 21B  = 5  ( B + S)(B - S)

The time taken by

them riding 14km downstream is equal to the time taken by them riding 6 km

=> 14/ (B + S)  =  6/(B - S)

=> 7/ (B + S)  =  3/(B - S)

=> 7B - 7S = 3B + 3S

=> 4B = 10S

=> 2B = 5S

=> B = 5S/2

or S = 2B/5

21B  = 5  ( B + S)(B - S)

=> 21B = 5 ( B + 2B/5)(B - 2B/5)

=> 21B = 5 ( 7B/5)(3B/5)

=> B = 5

S = 2

Boat speed in still water  =  5  km/hr

Speed of the river = 2 km/hr

Upstream speed = 5 - 2 = 3 km/hr

Downstream speed = 5 + 2 = 7 km/hr

Boat speed in still water  =  5  + 1 =  6 km/hr

Speed of river = 2 - 1 = 1 km/hr

Upstream speed = 6 - 1 = 5  km/hr

Downstream speed = 6 + 1 = 7 km/hr

Time = 42/5  + 42/7

= 8 hrs 24 mins + 6 hrs

= 14 hrs  24 mins

Learn More:

The difference between downstream speed and upstream speed is ...

brainly.in/question/8282434

a person goes 60 km upstream and downstream. time taken to cover ...

brainly.in/question/14866057