Q. 254.2( 6 Votes )

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Answer :

Let the speed of the stream be x km/hr

Speed of the boat upstream =( 20 – x )km/hr


Speed of the boat downstream =( 20 + x)km/hr


Distance =48km (given).


me taken in journey upstream =. hr


Time taken in journey upstream =hr


Time(upstream)-Time(downstream) =1hr (given)





96x=(20-x)(20 + x)


96x=400-x2


x2 + 96x-400=0


x2 + 100x-4x-400=0


x(x + 100)-4(x + 100)=0


(x-4)(x + 100)=0


Possible values of x are x=4 and x=-100


Rejecting the negative value of x,


Speed of stream =4km/hr


Or


(taking LCM)




-30=(x + 4)(x-7)


-30=x2-3x-28


X2-3x + 2=0


X2-2x-x + 2=0


x(x-2)-1(x-2)=0


(x-1)(x-2)=0


x=-1 or x=-2


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