A ship sails out to a mark at the speed of 15 km/h and sails back to the starting point at the speed of 10 km/h. The average speed of sailing of the ship is:
Explanation:
Let the distance between starting point and the mark be 150 kms.
Time taken to go to the mark = 150/15 = 10 hours Time taken to come back = 150/10 = 15 hours
∴ Average speed = (150 + 150)/(10 + 15) = 300/25 = 12 kmph
Hence,, option (a).