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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