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work problems

by resilient » Sat Mar 15, 2008 11:51 am
Stacy and heather are 20 miles apart and walk towards each other along the same route. STacy walks at a constant rate that is 1 mile per hour faster than heathers constant rate of 5 mph. If heather starts her journey 24 minutes later after stacy, how far from her original desintation has heather walked when the two meet?

qa is 8

to do this: manhattan gmat explains that one must set up a double rate chart.


Stacy heather total

R 6mph 5 mph -----

T t +.4 hours t hours -----

D 20-d miles d miles 20 miles


Obviously Stacy gets time plus a variable because she has been traveling longer. But the distance I dont understand. Why is Stacy's distance 20-d and heathers distance d.

Can they be switched back and forth?
How to know which one gets what distance?

Side note: other than og are there any sources to go to to master this topic!
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similiar question same concept

by resilient » Sat Mar 15, 2008 1:02 pm
Here is a similar question but same concept and question at hand.

one hour after andre started walking the 60 miles from x to y, james started walking from x to y as well. Andrew walks 3 mph and james walkes 1 mph faster than andre. How far from x will james be when he chatces up to andre?

to set up a variable chart in order to compute this. Manhattan gmat way!

andre james

d= (60-d)???? d= (d)????
r= 3mph r= 4mph
t= t=1 t= t


the success to these questions hinges on understanding how to chart these variables.. How do I know how to set up the distance variables. Is this right? Can they be interchanged?
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Re: work problems

by xeqtr » Sat Mar 15, 2008 1:30 pm
Pretty straightforward Engin Karde$ :)

since distance = time x speed

Heather will start 24 mins later, which means when they meet stacy will be walking for a time of "t + 0.4" hours and heather for t hours.

same for the distance when they meet heather would have walked d miles whereas stacy would have 20 - d. however you can switch them back or forth but this way the calculation will be easier trust me ;) I use a similar technique to this but this is good as well..just seen that

Enginpasa1 wrote:Stacy and heather are 20 miles apart and walk towards each other along the same route. STacy walks at a constant rate that is 1 mile per hour faster than heathers constant rate of 5 mph. If heather starts her journey 24 minutes later after stacy, how far from her original desintation has heather walked when the two meet?

qa is 8

to do this: manhattan gmat explains that one must set up a double rate chart.


Stacy heather total

R 6mph 5 mph -----

T t +.4 hours t hours -----

D 20-d miles d miles 20 miles


Obviously Stacy gets time plus a variable because she has been traveling longer. But the distance I dont understand. Why is Stacy's distance 20-d and heathers distance d.

Can they be switched back and forth?
How to know which one gets what distance?

Side note: other than og are there any sources to go to to master this topic!
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3rd question same cancept

by resilient » Sat Mar 15, 2008 2:31 pm
a bullet train leaves kyoto for tokyo travelling 240 mph at noon. Ten minutes later, a train leaves tokyo for kyoto traveling 160 mph. If tokyo and kyoto are 300 miles apart, at what time will the trains pass eachother?

a. 12:40
b. 12:49
c. 12:55
d. 1:00
e. 1:05


qa is b


The accompanying variable chart for this is:

K to T T to K Total

R 240 mph 160 mph -------

T t + 1/6 hrs t hrs -------

D 300-d miles d miles 300


My question is how to set up the bold REd? Are they interchangable? What is the rationale of setting this up?
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by xeqtr » Sat Mar 15, 2008 3:39 pm
yes it is interchangable, since depending on how you state, d will change and will have 2 different values.
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sometimes

by resilient » Sat Mar 15, 2008 3:51 pm
most of the time the setup doesnt even matter and the actual computations will matter. But it is still good to know and have in your pocket.
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Re: sometimes

by xeqtr » Sat Mar 15, 2008 3:54 pm
IMO it comes with experience to state it so. Since 160 x t = d is the simplest form..if you state it otherwise such that:

240 x (t + 1/6) = d, 160 x t = 300 - d..it's lil bit more complicated to substitute d to use in the other equation. That's why the author did it so I think..

K to T T to K Total

R 240 mph 160 mph -------

T t + 1/6 hrs t hrs -------

D 300-d miles d miles 300
Enginpasa1 wrote:most of the time the setup doesnt even matter and the actual computations will matter. But it is still good to know and have in your pocket.
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