Answer :

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

speed of river is given as 1 km/hr


speed of boat downstream = (x + 1) km/hr.


let time taken to go 112 km downstream = t



Now, speed of boat upstream will be (x – 1) km/hr.


let time taken to go 112 km upstream = T



Given that total journey time was 15 hr


t + T = 15




112x – 112 + 112x + 112 = 15x2 – 15


15x2 – 224x – 15 = 0


15x2 – 224x – 15 = 0


15x2 – (225 – 1)x – 15 = 0


15x2 – 225x + x – 15 = 0


15x(x – 15) + 1(x – 15) = 0



o r


And speed cannot be negative.


x = 15 km/hr.


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