YAA(lgebra)T: d=rt and systems of equations

[Saint Nick]

I find myself at the mercy of ATOT once again

I've been doing this problem for an hour and I can't figure it out... the answer is in the back of the book but I can't produce those answers at all. I'd love to list all that I've tried but it would take me an hours worth of work to do that, lol. Here's the problem:

A freight train and an express train leave towns 390 km apart, traveling toward one another. The freight train travels 30 km per hour slower than the expess train. They pass one another 3 hours later. What are their speeds?

So far all I've got is this equation:

x + y = 130 (Got that from 390 / 3, obviously! )

Thanks in advance to all those who prove helpful to my endeavor!

 

[Saint Nick]

I have to do something with 3x and 3y but I don't know what!!!

 

[eigen]

Oh christ...

Think about how you can express one trains speed in term of the other.

 

[iamwiz82]

t=3
speed of express=x

t(x+(x-30)) = 390

3(x +(x-30)) = 390

3x+3x-90=390

6x=480


x=80

freight is going 50

EDIT: I haven't taken algrebra in 8 or 9 years.

 

[Saint Nick]

well i tried that as well.

3x - 30 = 3y, right? tried it to no avail unless i did my math horribly wrong.

 

[Saint Nick]

Originally posted by: iamwiz82
t=3
speed of express=x

t(x+(x-30)) = 390

3(x +(x-30)) = 390

3x+3x-90=390

6x=480


x=80

freight is going 50

EDIT: I haven't taken algrebra in 8 or 9 years.

thank you wiz. i don't grasp math as well as most others. to be honest i think i have ADD. i should make another thread about that... but thanks again you helped a lot, i get it now.

 

[2cpuminimum]

You have two variables, x, and y. Your problem is that you only wrote down one equation. You need a number of equations equal to the number of variables in order to solve. It's all about following standard problem solving procedure. You just needed to take the information given in words and make one more equation from the given info.