Hi all,

Page 29 of the MGMAT WT guide (2007 Edition) has an example at the top that reads as follows:

Stacy and Heather are 20 miles apart and walk toward each other along the same route. Stacy walks at a constant rate that is 1 mph faster than Heather's constant rate of 5mph. If Heather starts her journey 24 minutes after Stacy, how far from her original destination has Heather walked when the two meet?

My question is regarding setting up the R=TD formula for Stacy and Heather. The way the book solves for it is to set up the equations as follows:

Stacey Heather
R 6 5
T t+.4 t
D 20-d d

However, can I still obtain the right answer if I set things up as follows:

Stacey Heather
R 6 5
T t+.4 t
D d 20-d

If not, why?

Thanks!

You absolutely can get the right answer that way. But you open up the possibility that you'll make a careless mistake, so I'd recommend doing it the way the book does it.

Here's why: they ask us for Heather's distance. If we set Heather equal to plain d, then when we solve, we're done - d is the answer. If we set Stacy equal to plain D, though, then we have to do an extra step at the end: 20-d. I absolutely guarantee you that, on a problem of this type, Stacy's distance is also going to be in the answer choices. So if you forget that last step, you'll pick Stacy's distance instead of Heather's... and you'll get the problem wrong.

Moral of the story: always try to set things up so that you're solving for what they asked!