Given :
Total distance travelled =100m
Time taken to cover 60m distance :
Time=distance/speed or displacement/time
=60/20
=3sec
Time taken to cover next 40m :
time=distance/speed or displacement/time
=40/10
=4sec
Total time=3+4=7sec
Average velocity=Total displacement/magnitude of distance]/total time
=100m/7sec
=14.28m/s
∴The average velcoity =14.28m/s