Question

the speed of a boat in still water is 8 km/hr and the speed of the stream is 2km/hr . the boat is rowed upstream for a certain distance and then taken back to starting point . find the average speed for the whole journey.

Answer 1

Heya,

Let the distance be x

Speed of boat upstream = 8 km/hr - 2 km/hr = 6 km/hr

Time taken to go upstream = x/6 hr

Speed of boat in downstream = 8 km/hr + 2 km/hr = 10 km/hr

Time taken by boat to go downstream =
x/10 hr

Total distance covered = x+x = 2x

Total time taken = x/6 + x/10 =
$\frac{5x + 3x}{30}$
= 8x/30

= 4x/15

Average speed =

$\frac{2x}{ (\frac{4x}{15}) }$

$= \frac{2x \times 15}{4x}$
= 15/2 = 7.5 km/hr

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Answer 2

Answer:

7.5 km/h is write answer....