Question

if a boat takes 11 hours to travel in upstream 28 km and 40 km in downstream.and it takes 12 hours to travel 36 km in upstream and 30 kilometre in downstream find the speed of the boat and stream.​

Answer 1

Answer:

speed of the boat in still water is 7 km/hr.

speed of the stream is 3 km/hr

Step-by-step explanation:

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

Let the speed of the stream be y km/hr

The speed of the boat downstream = (x+y) km/hr

The speed of the boat upstream = (x−y) km/hr

Time = Distance / Speed

11 hours to travel 28km upstream and 40km downstream.

11 = 28/ (x-y) + 40/(x+y)

12 hours to tavel 36km upstream and 30km downstream.

12 = 36/(x-y)  + 30/(x+y)

let  1/(x-y) = a and 1/(x+y) = b

=> 11 = 28a+40b

similarly  12 = 36a+30b

by solving both

a= 1/4

b= 1/10

a= 1/(x-y) = 1/4

b= 1/(x+y) =1/10

=> 4 =x- y

10 = x+ y

x= 7km/h

y= 3 km/h