Question

some foreign tourists observed that a boat goes 30km upstream and 44 km downstream in 10 hours. the same boat goes 40 km upstream and 55 km downstream in 13 hours. speed of boat in still water is 8.5 km/hr and the speed of stream is 3.8 km/hr.{ use elimination method }.


thank you :)

Answer 1

★ PAIR OF LINEAR EQUATIONS IN TWO VARIBLES ★

Let the speed of the stream be = u kmph

And, Let the speed of the boat be = v kmph

 

So, Speed upstream will be = v - u  kmph

And, Speed downstream will be =  v + u  kmph

 

Now, 30 km  upstream in time duration  =   30 / (v - u)  hrs

And, 44 km  down stream in time duration  =  44 / (v + u)  hrs

 

    44 / (v + u)  + 30 / (v -u)  = 10 hrs     → (1)

 

Similarly, 40 /(v - u)  + 55 / (v +u)  = 13 hrs        

 

Multiply with 3/4:  

     

We get, 30/(v-u) + 165 / 4(v+u) =    39/4        →  (2) 

 

Now (1) - (2),

 

We get,  [44 - 165/4] / (v+u) = 10 - 39/4 = 1/4

        ⇒   v + u = 11      →  (3)

 

Substitute this in (1) to get: 

 

   So, 44/11 + 30/(v-u) = 10

 ⇒  v - u = 30/6 = 5      →  (4)

 

Solving  (3) and (4) ,  We get : 

 

∴ v = 8 kmph  and u = 3 kmph

Answer 2

Answer:

Step-by-step explanation:

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