Multiple choice

In 3 hours Amit can go 21 km along the current and 15 km against the current in the same time. What is the speed of the current? अमित धारा के साथ 3 घंटे में 21 किमी जा सकता है और उसी समय में धारा के विरूद्ध 15 किमी जा सकता है। तो धारा की चाल क्या है?

  1. 1 km/hr/किमी/घं.

  2. 2 km/hr/किमी/घं.

  3. 2.5 km/hr/किमी/घं.

  4. 4 km/hr/किमी/घं.
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A Correct answer
Explanation

Downstream speed = 21/3 = 7 km/h, upstream speed = 15/3 = 5 km/h. Speed of boat = (downstream + upstream)/2 = 6 km/h. Speed of current = (downstream - upstream)/2 = 1 km/h. The current's speed is half the difference between downstream and upstream speeds.

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