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Rate problem MGMAT answer - don't get the logic

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baileysnowflake: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sat Jun 05, 2010 8:06 am

by baileysnowflake » Sun Jun 06, 2010 6:15 am

Hi,

I am going through MGMATs book Word Translations (4th ed) page 46 and am stuck on I am sure what is an easy problem. The question is Q5 "One hour after Adrienne started walking the 60 miles from X to Y, James started walking from X to Y as well. Adrienne walks 3 miles per hour, and James walks 1 mile per hour faster than Adrienne. How far from X will James be when he catches up to Adrienne?"

I am fine with the answer but a little confused by the explanation in the book where it tells you to that Adrienne's time is (T+1) and James time is (T) and then to substitute the equations.

Can anyone explain the logic for doing this? I'd really appreciate the help.
Thanks

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Source: Beat The GMAT — Quantitative Reasoning | Sun Jun 06, 2010 6:15 am

mj78ind: Master | Next Rank: 500 Posts; Posts: 265; Joined: Mon Dec 28, 2009 9:45 pmFollowed by: 2 members; Thanked: 26 times; GMAT Score:760

by mj78ind » Sun Jun 06, 2010 9:23 am

If we assume James has walked for 'T' hours then Adri has walked for 'T+1' per the stem of the question. Essentially Adri has an hour's lead on James.

These questions usually are of the form that one guy who starts late walks fast and catches upto the other guy who has a lead. This could happen for people reading books, going around circular courses, up and downstream in a boat ........

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baileysnowflake: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sat Jun 05, 2010 8:06 am

by baileysnowflake » Mon Jun 07, 2010 5:14 am

Hi, Thank you for getting to back to me. I do understand to apply the formula you add T+1 which is one hour more, but it's the substitution itself I don't get.

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mj78ind: Master | Next Rank: 500 Posts; Posts: 265; Joined: Mon Dec 28, 2009 9:45 pmFollowed by: 2 members; Thanked: 26 times; GMAT Score:760

by mj78ind » Mon Jun 07, 2010 7:09 am

baileysnowflake wrote:Hi, Thank you for getting to back to me. I do understand to apply the formula you add T+1 which is one hour more, but it's the substitution itself I don't get.

@bailey

Sorry do not have the MGMAT book. But here is what I would do ........
Distance traveled by Adri in 1 hour = 3 miles
James covers the 'gap' in 3 hours. Hence Adri has walked for 4 hours, i.e. 3*4 = 12 miles and James has also walked = 4*3 = 12 miles (Since Jame's speed is 4 mph)

If still unclear can set up a Gtalk call and walk you through this.

Cheers

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