Answers

2015-05-02T06:55:46+05:30
given that ,
    1st 30 km uniform speed is (u1) = 40 km/h 
     2nd 30 km uniform speed is ( u2 ) = 20 km/h
     total distance ( d ) = 30 + 30 = 60 km
     time taken in 1st time = d / t = 30/40 also, 3h / 4 = 180/4 = 45 min
     tim taken in 2nd time = d/t = 30/20 also, 3h/2 = 180/2 = 90 min
    total time = 45 + 90 = 135 min = 135/60 h
av.speed = 60/135/60 = 60 * 60 /135 = 26.66 km/h ( answer )    
  
 
 
    
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2015-05-03T09:36:28+05:30


V1=40kmph

V2=20kmph

A.V=2V1V2/V1+V2

      =2x40x20/60

       =26.67kmph

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