One-fourth of a certain journey was covered at an average speed of 45km/hr :

One-fourth of a certain journey was covered at an average speed of 45km/hr; one third at the speed of 48 km/hour and the remaining journey at the speed of 50 km/ The average speed of the whole journey in km/hour. is

  1. 54
  2. 51
  3. 48
  4. 46
Anurag Mishra Professor Asked on 23rd January 2016 in Maths.
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  • 1 Answer(s)

    Answer: (3) 48 

    Explanation:-
    Let the distance covered by whole journey be X km
    Then, distance covered in the remaining journey = X – (X /4 + X/3)
     = X – (3 X + 4 X)/12
    = (12 X – 7 X)/12
     = 5 X/12

    Formula-
    The average speed = Total distance covered/total time taken
     

    Then, X/[X/(4/45) + X/(3/48) + 5 X/(12/50)]
    = X/X[1/180 + 1/144 + 1/120]
    = 1/(1/15 + 1/12 + 1/10)/12
     = 12/(4 + 5 + 6)/60
     = 12 x 60/15
     = 12 x 4
     = 48 kms/hr

    Then, the average speed of the whole journey is 48 kms/hr.

    Hence, the correct answer is option (3) 48. 

    Anurag Mishra Professor Answered on 23rd January 2016.
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