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23. A motor boat whose speed is 35 km/hrin still water takes 3 hour more to go100 km upstream then to returndownstream to the same spot. Thespeed of the stream is​

Answer»

Answer:

15

Step-by-step explanation:

Let the speed of STREAM be x

Time upstream = 100/35-x

Time DOWNSTREAM = 100/35+x

100/35-x  - 100/35+x = 3    

100(35+x) - 100(35-x) = 3(35² - x²)

3500+100x - 3500 + 100x = 3675 - 3x²

3x² + 200X - 3675 = 0  

DISCRIMINANT =200²+210²= 40000+44100=84100

x = -b±√84100/ 2A

=  -200±290/ 2*3

= 90/6 or -490/6

= 15 or -490/6

Speed of stream = 15 (speed cannot be negative)



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