# 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

- 54
- 51
- 48
- 46

**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.