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a boat travels 30 km in still water. If this boat goes upstream in a river flowing at a rate of 12 km/h for 5km, and then returns back downstream to its starting point, what is the average speed for the whole trip in km/h?

 

Would appreciate a reply! Thanks for reading

 Oct 13, 2020
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Total distance is 5 + 5 km = 10 km

 

tu =  5 / ( 30-12)  = 5/18

td = 5 / (30+12)   = 5/42

 

total distance / total time = average km/hr  

    10 /( 5/18 + 5/42)  = 10 / (300/756)  = 7560/300 = 25.2 km/hr

 
 Oct 13, 2020

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