Answers

2015-06-27T13:09:14+05:30
For first half, distance=v1t/2.........for second half, distance=v2t/2
Average speed=v1t/2+v2t/2 the whole divided by t/2+t/2

                     =v1t+v2t/2/t
                     =v1+v2/2
 
                       80+40/2 = 60 km/h 
   
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