a man travels certain distance by boat downstream at 30 km/hr and return upstream at 41 6m/s. what is the average speed of his travel?
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30 km/hr is clear enough, but what does “41 6m/s” mean? Multiplying it by 3.6 to convert to km/hr, it's either 1497.6, 149.76, or 14.976 km/hr.
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Given:
A man travels certain distance by boat downstream at 30 km/hr and return upstream at 41 6m/s.
To find:
What is the average speed of his travel?
Solution:
From given, we have,
The downstream speed = 30 km/hr
The upstream speed = 4 1/6 km/hr = 25/6 km/hr
Speed in still water = (downstream + upstream)/2 = [ 30 + 25/6 ] / 2 = 205/12 km/hr
Average speed = ( downstream × upstream) / speed in still water
= (30 × 25/6) / (205/12)
= 5 × 25 × 12 / 205
= 300/41
= 7 31/41 km/hr
Therefore, the average speed of a man's travel is 7 31/41 km/hr
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