# Average Speed

• Jul 24th 2009, 06:14 AM
magentarita
Average Speed
If I drive x mph for t hours and then y mph for 2t hours, what is the expression for average speed?

I know the average speed = distance/time but that's where I get stuck.
• Jul 24th 2009, 06:47 AM
Quote:

Originally Posted by magentarita
If I drive x mph for t hours and then y mph for 2t hours, what is the expression for average speed?

I know the average speed = distance/time but that's where I get stuck.

Hi . You will need to look for the total distance first .

Use the formula s=vt (ie s=xt and s=y2t)

average speed = (xt+y2t)/(2t+t)
• Jul 24th 2009, 06:48 AM
CaptainBlack
Quote:

Originally Posted by magentarita
If I drive x mph for t hours and then y mph for 2t hours, what is the expression for average speed?

I know the average speed = distance/time but that's where I get stuck.

$d=x\times t+y \times 2t$

$t=t+2t=3t$

$\overline{v}=\frac{xt+2yt}{3t}$

CB
• Jul 24th 2009, 06:49 AM
songoku
Quote:

Originally Posted by magentarita
If I drive x mph for t hours and then y mph for 2t hours, what is the expression for average speed?

I know the average speed = distance/time but that's where I get stuck.

Find the distance covered when you drive x mph for t hours and y mph for 2t hours, then add them to get total distance

EDIT : a minute late from CB and two minutes from mathaddict...
• Jul 24th 2009, 06:49 AM
yeongil
Quote:

Originally Posted by magentarita
If I drive x mph for t hours and then y mph for 2t hours, what is the expression for average speed?

I know the average speed = distance/time but that's where I get stuck.

Or... d = rt.

If you drive x mph for t hours, then the distance traveled is xt miles.
If you drive y mph to 2t hours, then the distance traveled is 2yt miles.
Total distance: xt + 2yt.
Total time: t + 2t = 3t.

Average speed:
$\frac{xt + 2yt}{3t} = \frac{x + 2y}{3}$

01

Edit: beaten to it by three people! (Rofl)
• Jul 24th 2009, 06:53 AM
songoku
Quote:

Originally Posted by yeongil
Edit: beaten to it by three people! (Rofl)

LOL !!
even i'm surprised when i know you also give the answer
• Jul 24th 2009, 12:36 PM
magentarita
Thanks..
I want to thank all of you.