Question

please answer this question

Answer 1

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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Answer 2

time taken to travel the first 40 km = 1 h  

taken to travel the next 30 km = 30/20= 1.5 h

distance travelled = 40 + 30 = 70

time taken = 1 + 1.5 = 2.5 h

Average speed = 70 / 2.5

                           = 28 km/h