A train travells a distance with a speed of 30km/hr and returns with a speed of 50km/hr.Find average speed?

Question

average speed=initial speed+final speed
----------------------------------------------------------------
Total time taken

Answer 1

the average speed in such questions is the harmonic mean and not arithmetic mean. arithmetic mean of 50 n 30 is
(50+30)/2 = 40 but this ans is wrong.

avg speed is harmonic mean=
2 X (50 X 30 )
-----------------
( 50 + 30 )

= 37.5 km/hr

formula used:

2
---
hm
=
1+1
-- --
a b

=>
hm=
2(a X b )
---------
a+b

Answer 2

This is badly stated, but presumably "travels a distance and returns" implies travels a certain distance x in one direction, and then travels the same distance in the opposite direction. The direction doesn't matter, we can just as well say that the train traveled x miles at a speed of 30km/hr and then another x miles at a speed of 50km/hr.

Contrary to a previous poster, this is as simple as adding and averaging: the average speed is (30*x+50*x)/(2x), or, dividing through, (30+50)/2 km/hr = 40km/hr.

Answer 3

lemme tell u---=total distance covered/total time taken

let distance be 'y'.
time take to cover y dis by 30km/hr=y/30
time take to cover y dis by 50km/hr=y/50
total time=3y+5y/150=8y/150
now total distance (coming and going)=2y
now, =2y*150/8y=37.5km/hr

seee soo simple (childs play) just apply direst physics concepts...approach should be correct!!!!

Answer 4

say the distance is x.
so the time take while going is x/30hrs
and time taken while coming back is x/50hrs
adding them we get total time = 8x/150 hrs

now this much time was taken while travelling 2x distance, so the average speed is 2x/ (8x/150) = 37.5km/hr

average speed = diatence / time
(... your assumption is wrong)

Answer 5

Give it a break! Those questions are NEVER made so simple you just add the two numbers and divide by two. Double check the question.

Answer 6

40km/hr took 2 seconds.

Answer 7

40km/hr

Answer 8

40km/hour