Question

A person travelled with a speed of 50kmph for 1hr and with 20kmph for next 2hrs. find the average speed for whole journey?

Answer 1

Solution:-

In 1 Hour he Walked 50 km & 20km for next 2 Hours.

Averag Speed = Total Distance Travelled/ Total Time Taken

Total Distance Travelled = 50 for 1 hr + 20 for 2 hr

=> Total Distance = 50×1 + 20×2

=> Total Distance = 50 + 40

=> Total Distance = 90 km.

Total Time Taken = 1 hr + 2 hrs.

=> Total Time Taken = 3 hours.

Hence,

Average Speed = Distance Travelled/Time Taken

=> Average Speed = 90/3

=> Average Speed = 30 km/hr.

Answer 2

$\bold{Case\:I}$ : Given that,

Speed = 50 Kmph

Time taken = 1 hr

.°. Distance travelled, D = speed × time taken

=> D = 50 kmph × 1 hr

=> D = 50 km

$\bold{Case\:II}$ : Given that,

Speed = 20 Kmph

Time taken = 2 hrs

.°. Distance travelled, D' = speed × time taken

=> D' = 20 kmph × 2 hrs

=> D' = 40 Km

Now,

total distance covered = D + D'

=> Total Distance covered = (50+40) Km

=> Total Distance covered = 90 Km

and,

Total time taken = (1+2) hrs

=> Total time taken = 3 hrs

.°. Speed for whole journey= $\frac{Total\:distance\:covered}{Total\:time\:taken}$

=> Speed for whole journey = $\frac{90\:km}{3\:hrs}$

Hence,

Speed for whole journey = $\bold{30\:Kmph}$