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Chris & Charlie

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by gmatmachoman » Tue Mar 30, 2010 8:58 pm
One hour after Chris leaves her home, Charlie leaves his home to intercept her. If
Charlie travels twice as fast as Chris, how long will it take Charlie to intercept Chris?

(1) Chris lives 90 miles due south of Charlie
(2) Charlie's rate is 30 mph

OA:Follow soon
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by pops » Tue Mar 30, 2010 9:32 pm
gmatmachoman wrote:One hour after Chris leaves her home, Charlie leaves his home to intercept her. If
Charlie travels twice as fast as Chris, how long will it take Charlie to intercept Chris?

(1) Chris lives 90 miles due south of Charlie
(2) Charlie's rate is 30 mph

OA:Follow soon
Important thing to note here is which direction chris left is not known (it might be towards charl's home or away from charl's home or may be east or west)
So, even after knowing the distance between both houses and speed we wont be able to answer the question.

Now, if we think that since it is asked that how long charlie take to intercept her.. assume chris is going away from charlie's home ..the same line as chris-charlie home..
Let D be distance between Chris and Charlie's home..
charlie has to travel D miles more than chris in T-1 hours (T: time walked by Chris till Charlie intercepts her)
let chris speed be x, charlie = 2x
hence, 2x*(T-1) = x*T + D
=> x(T-2)=D
hence, we need x: speed and D: distance between home to find out T

So, we need both the statements to answer. (Important to note the direction where Chris started is assumed away here)
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by ajith » Tue Mar 30, 2010 10:32 pm
gmatmachoman wrote:One hour after Chris leaves her home, Charlie leaves his home to intercept her. If
Charlie travels twice as fast as Chris, how long will it take Charlie to intercept Chris?

(1) Chris lives 90 miles due south of Charlie
(2) Charlie's rate is 30 mph

OA:Follow soon
I go for C too

1. We have the distance not the speeds
2. We have the speeds but we do not know the distance [if the distance is short charlie may never catch up with Chris]

Combining,
we have the distance as well as the speeds, i think it would be sufficient
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by ajith » Tue Mar 30, 2010 10:35 pm
On second thoughts, Do they travel in straight line?

If they do do they travel towards each other in the shortest distance?


These are assumed!
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by pops » Tue Mar 30, 2010 11:43 pm
ajith wrote:On second thoughts, Do they travel in straight line?

If they do do they travel towards each other in the shortest distance?


These are assumed!
Even if they travel towards each other we would be able to get the time with both the conditions together :)
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by gmatmachoman » Wed Mar 31, 2010 2:37 am
ajith wrote:On second thoughts, Do they travel in straight line?

If they do do they travel towards each other in the shortest distance?


These are assumed!
IS it mentioned anywhere that they travel in same direction or else in opposite direction or is there a bridge that could shorten the distance..??

So can u plz review ur answer???@ Ajith , I liked ur thought process man!!
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by gmatmachoman » Wed Mar 31, 2010 2:38 am
pops wrote:
ajith wrote:On second thoughts, Do they travel in straight line?

If they do do they travel towards each other in the shortest distance?


These are assumed!
Even if they travel towards each other we would be able to get the time with both the conditions together :)
DS looks for definite answer & not a Assumed ones!! SO plz review ur answers!
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by pops » Wed Mar 31, 2010 3:20 am
my answer stays as it is. At first I mentioned that what is lacking in the question is which direction Chris started walking. without that knowledge we cant answer the question with both the statements.

However, if the question would have suggested that they travel in the same line (either same or towards each other) then both the conditions are required to answer.
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by Fiver » Wed Mar 31, 2010 5:02 am
gmatmachoman wrote:One hour after Chris leaves her home, Charlie leaves his home to intercept her. If
Charlie travels twice as fast as Chris, how long will it take Charlie to intercept Chris?

(1) Chris lives 90 miles due south of Charlie
(2) Charlie's rate is 30 mph

OA:Follow soon
Choose E.

Assume that Chris' speed is x units/hr, and hence Charlie's speed is 2x units/hr.

If Chris and Charlie were to leave the same house, then the answer would have been 1 hour.
x/2x-x = 1 hr.

Keeping this in mind all we need to know only one thing, immaterial of the direction et all :

How much time did Charlie take to reach Chris' home? Let's call this 't'

Both the statements together may give different values of 't', depending upon the direction chosen by Charlie.
Hence the final answer will vary accordingly, because based on 't', distance covered by Chris will vary and as a derivative our answer too.

What's the OA?
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by Stuart@KaplanGMAT » Wed Mar 31, 2010 10:22 am
The answer is definitely E.

As noted by others (but without doing any math), we can see that if Chris travels directly toward Charlie the intercept time will be a lot less than if Chris travels directly away from Charlie. Chris could also travel in an infinte number of other directions, leading to other solutions to the problem.

So, unless we know Chris's direction (and, to be complete, Charlie's direction as well - does he travel in a straight line? Does he have to follow certain roads? etc...), we can't solve.
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