Multiple choice

A man goes 12 km upstream and back again to the starting point in 4 hours. If the speed of water is 4 km/hr. Find the speed of the boat. एक आदमी 12 किमी.ऊर्ध्वप्रवाह जाता है और प्रारम्भिक बिंदु पर आने में 4 घंटे लेता है | यदि जल की गति 4 किमी./घंटा है | नाव की गति ज्ञात कीजिये |

  1. 6.5 km./किमी.

  2. 7 km./किमी.

  3. 8 km./किमी.

  4. 5 km./किमी.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let boat speed = b. Upstream speed = b - 4, downstream speed = b + 4. Total time: 12/(b-4) + 12/(b+4) = 4. Solving gives b = 8 km/hr. Check: 12/4 + 12/12 = 3 + 1 = 4 hours.

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