Multiple choice

If a boat goes 100 km downstream in 10 hours and 75 km upstream in 15 hours, then the speed of stream is- यदि एक नाव 10 घंटें में धारा की दिशा में 100 किमी. चलती है और धारा के विरूद्ध 15 घण्टों में 75 किमी. चलती है, तो धारा की चाल कितनी है?

  1. 2 km/hr./किमी/घं.

  2. 3 km/hr./किमी/घं.

  3. 2.5 km/hr./किमी/घं.

  4. 3.5 km/hr./किमी/घं.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Downstream speed = 100/10 = 10 km/hr, Upstream speed = 75/15 = 5 km/hr. Let boat speed = b, stream speed = s. Then b + s = 10 and b - s = 5. Adding: 2b = 15, so b = 7.5 km/hr. Subtracting: 2s = 5, so s = 2.5 km/hr.

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