Question

A body can have 0 average velocity but not 0 average speed ? Why?

Answer 1

Average velocity is defined as the ratio of total displacement by TOTAL time taken.Average speed is the ratio of total distance by TOTAL time taken.As average velocity depends on displacement and displacement can be zero if the object returns to initial position .Where as distance can never be zero for a journey.
Example:A person completes one revolution in circular path. Distance = 2 *pi*rWhereas displacement is zero as source and destination is same.
Hence A body can have zero average velocity but not zero average speed.

Answer 2

HY THERE A BODY CAN HAVE AVERAGE VELOCITY ZERO BCOZ 
VELOCITY MEANS RATE OF CHANGE OF DISPLACEMENT IF THE INITIAL AND FINAL POSITION OF THE BODY IS SAME THEN AVERAGE VELOCITY CAN BE ZERO 
LET ME GIVE YOU AN EXAMPLE..................................................
RAM TRAVELS 10 M FROM HIS SHOP TO HOME THEN AFTER PURCHASING HIS REQUIREMENTS HE COMES  BACK TO HOME IN 15 MINS....................
HERE FINAL AND INITIAL POSITION BOTH ARE SAME THEN THE AVERAGE VELOCITY IS ZERO BUT AVERAGE SPEED WILL BE 10 +10/15+15 = 20/30 = 2/3 SO AVERAGE SPEED CANNOT BE ZERO.................................................
THANKS .................