A boat goes 28 km downstream and while returning covered only 75% of distance covered in downstream. If boat takes 3 hour more to cover ups… — Answer & Discussion

A boat goes 28 km downstream and while returning covered only 75% of distance covered in downstream. If boat takes 3 hour more to cover upstream than downstream, then find the speed of boat in still water (km/hr) if speed of current is 5/9 m/sec.

A3 km/hr
B4 km/hr
C5 km/hr
D6 km/hr

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Discussion 1

CCommunity05 Jun 2019

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

Speed of the stream = 5/9 m/s = 2 km/hr

Speed of downstream = (x + 2) km/hr

Speed of upstream = (x - 2) km/hr

(0.75 × 28)/(x – 2) – (28/(x + 2)) = 3

21/(x – 2) – 28/(x + 2) = 3

21x + 42 – 28x + 56 = 3x2 – 12

3x2 + 7x – 110 = 0

3x2 + 22x – 15x – 110 = 0

3x (x – 5) + 22(x – 5) = 0

⇒ x = 5