A ship sails out to an island at the rate of 15 km/h and sails back to the starting point at 10 km/h. Find the average sailing speed for the whole journey.
Given,
Speed of ship in sailing direction (x) = 15 km/h
Speed of ship in sailing back (y) = 10 km/h
So, By using direct formula,
Average speed of ship in whole journey = 
Hence, Average speed of ship = 12 km/h
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