# Average Speed Formula

How would one write a formula to find the average speed if one knows the distance traveled and the rate of speed for each portion of the trip?

20 miles at m speed
40 miles at n speed

 manimuth Posts: 262, Reputation: 299 Full Member #2 Apr 15, 2007, 07:54 PM
Here's a hint: The units for average speed is m/h (miles/hour[or any other unit of time, really]), right? So... get the total miles over the total time. (How? It's your homework )

What? You don't know the hours? If I went at a speed of 60 miles/hour for 60 miles, how long did I travel? If you said 1 hour you are right. Use the same logic.

Good luck.
 ljackson30 Posts: 2, Reputation: 1 New Member #3 Apr 16, 2007, 04:34 AM
I don't know the speed nor the time. All I am given is the distance.
 Capuchin Posts: 5,319, Reputation: 3601 Uber Member #4 Apr 16, 2007, 04:45 AM
You need to work out total distance divided by total time. You have plenty enough information to do that. You ARE given the speed...

Speed = distance/time will giv eyou the answer.
 GUESTS 9 Posts: n/a, Reputation: Guest #5 Apr 8, 2008, 07:32 PM
average speed = delta distance divided by delta time

vav = dd / dt

ps. D = delta
 punkmax Posts: 1, Reputation: 1 New Member #6 May 7, 2008, 05:05 AM
Is the answer for the average speed like this:

3nm/(n + 2m) ?

Thanks.

Quote:
 Originally Posted by ljackson30 How would one write a formula to find the average speed if one knows the distance traveled and the rate of speed for each portion of the trip? 20 miles at m speed 40 miles at n speed
 j199279 Posts: 2, Reputation: 10 New Member #7 Aug 19, 2009, 01:32 PM
60
------
2m+n

Because

You know that the formual for average speed?
So
You can get
20+40
--------
t1+t2
But you don't know t1 and t2

To find time
The formula is d/r
Now you can substitute

20+40
-------------
20/m+ 40/n

Which is 60/20n+40m
 j199279 Posts: 2, Reputation: 10 New Member #8 Aug 19, 2009, 01:34 PM

Sorry I got a mistake which is the first part
Just ignore below this

60
------
2m+n
 dnkulkarni Posts: 1, Reputation: 10 Junior Member #9 Oct 18, 2009, 10:38 PM
ans : if the distances are considered as d1 and d2 and speed as s1 and s2 then average speed =

= (d1 + d2 ) / ( d1 / s1 + d2/s2 )

if d1 = d2 i.e. over same distance then

avg speed = 2 S1* S2 / (S1 + S2)
 kmpm Posts: 3, Reputation: 1 New Member #10 Nov 17, 2009, 06:00 AM

100m (Distance) 44 sec (time)=Speed

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