Multiple choice

A boat goes 6 km upstream and 6 km downstream in 4 hour. The same boat goes 18 km downstream and 4 km upstream in 5 hours. What is the speed (in km/hr) of boat in still water? एक नाव 4 घंटे में 6 किमी धरा के विपरीत तथा 6 किमी धरा के साथ यात्रा है। वही नाव 5 घंटे में 18 किमी धरा के साथ तथा 4 किमी धरा के विपरीत यात्रा करती है। पानी में नाव की गति (किमी / घंटा में) ज्ञात कीजिए?

  1. 8

  2. 4

  3. 6

  4. 5
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let boat speed in still water be b km/hr and stream speed be s km/hr. Upstream speed = (b-s) km/hr, downstream speed = (b+s) km/hr. From the first trip: 6/(b-s) + 6/(b+s) = 4. From the second trip: 18/(b+s) + 4/(b-s) = 5. Solving these equations gives b = 4 km/hr. Option B is correct.

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