Car X is 40 miles west of Car Y

[danielle.wipperfurth]

5th Ed. Word Problems, p. 35

I understand how to solve this problem using a combined equation (.5r x 8/3 = 40) but wanted to see if solving in a more traditional way would work too. I tried solving one of the two equations for d and plugging it into the other and kept coming up with a negative number.

1st two equations:
3/2r x 8/3 = d
r x 8/3 = d + 40

Solve for d:
d = 8/3r - 40

Plug into the other one:
8/3r - 40 = 3/2r x 8/3
8/3r - 40 = 4r
40 = -4/3r
-30 = r

Should solving for d and plugging it into the other equation work (i.e. did i just make a misstep in my algebra to end up with a negative answer) or is a singular equation the only way to solve for this?

[tim]

actually, there's a typo in the book. they swapped the d and d+40. put them back in the correct order, and that should clear up the problem you're having..

[khushbumerchant]

I have a query. How did they get 8/3 as time here?? m bit lost.

[RonPurewal]

Hello all,

Per the forum rules, the entire text of the problem must be posted. This thread should not have received a response from us without the text of the problem.

Please post the full text of the problem -- including the answer choices, if there are any. Thanks.