1.

Mikha can row at a speed of 15/2 km/h in still water. If he takes twice the time to row a distance upstream as to row the same distance downstream, then what will be the speed of the stream (in km/h)?1. 4.5 km/h2. 2.5 km/h3. 6.5 km/h4. 5.5 km/h5. None of the above

Answer» Correct Answer - Option 2 : 2.5 km/h

 

Calculations:

Let the speed of the stream be x km/h

∴ Rate upstream = 15/2 – x

And rate downstream = 15/2 + x

Let's also assume the time taken downstream and upstream is 1 hr and 2 hrs respectively. 

Distance = Speed × Time

∴ (15/2 + x) × 1 = (15/2 – x) × 2

⇒ 15/2 + x = 15 - 2x

⇒ 15 + 2x = 30 - 4x

⇒ 6x = 15

⇒ x = 2.5 km/h

The speed of stream is 2.5 km/h.



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