3 Connecting Flights

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kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 amFollowed by: 1 member; Thanked: 16 times

by kanha81 » Wed Feb 11, 2009 4:55 pm

Grateful if you can please explain the answer mathematically (prolly tabular format) instead of verbally. This is just a suggestion. I am looking for an alternative and quicker way to analyze and solve the problem. I found the verbatim too hard to follow.

An Airline passenger is planning a trip that involves 3 connecting flights that leave from airport A, B, C resp. The first flight leaves Airport A every hour beginning @ 8:00 AM; & arrives at Airport B 2 1/2 hours later. The second flight leaves Airport B every 20 minutes, beginning @ 8:00 AM & arrives at Airport C 1 1/6 hours later. The third flight leaves Airport C every hour, beginning @ 8:45 AM. What is the least total amount of time the passenger must spend between flights if all flights are to keep schedule?

(a) 25 mins
(b) 1 hr 5 mins
(c) 1 hr 15 mins
(d) 2 hr 20 mins
(e) 3 hr 40 mins

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Source: Beat The GMAT — Problem Solving | Wed Feb 11, 2009 4:55 pm

DeepakR: Master | Next Rank: 500 Posts; Posts: 158; Joined: Tue Sep 30, 2008 8:47 amFollowed by: 1 member; Thanked: 23 times; GMAT Score:660

by DeepakR » Wed Feb 11, 2009 5:19 pm

A..........................B Time taken = 2hrs 30 mins starting at 8:00 AM @A running for every 1 hr.

B..........................C Time taken = 1*1/6 hr = 1hr *(1*60/6)=1hr 10 min
running for every 20 mins starting @8:00AM @B

C..........................someplace runs every 45 minute starting from @8:45AM

Now solution:

Step1: You start from A @8:00 AM and reach B @10:30AM.

Step2: The next immediate flight @B is only @10:40AM since the flight runs for every 20 mins @B.

So there is a delay of 10 mins @B

Step3: You leave from B @10:40 and reach C @11:50.

Step4: The next immediate flight @C is only @12:45PM. So you have to wait for another 55 mins at airport C.

So total time you need to wait = 10 min @B + 55 min @C = 65 mins = 1hr and 5 mins

Ans.) B

-Deepak

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dellaboemia: Junior | Next Rank: 30 Posts; Posts: 27; Joined: Sun Oct 16, 2011 2:34 pm; Thanked: 2 times

by dellaboemia » Sat Mar 17, 2012 11:42 am

This optimization problem just happened to work out to allow the traveler the minimum wait time if he took the first flight. What if that had not been the case? We would be required to experiment with various departure time options, aligning various schedules, etc... Hardly a problem that (I) could solve in 5 minutes, let alone 2.

Is there a method for evaluating the options mathematically or algebraically, without slogging through various departure time options? Is there some airline industry formula used to calculate various optimization scenarios?

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serendipiteez: Junior | Next Rank: 30 Posts; Posts: 25; Joined: Wed Feb 13, 2013 9:25 pm; Thanked: 2 times

by serendipiteez » Tue May 28, 2013 4:38 am

This is insane. How can you solve this in under 2 minutes?

There must be a faster way. Experts would really appreciate if you could shed some light on this.

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Tue May 28, 2013 6:32 am

serendipiteez wrote:This is insane. How can you solve this in under 2 minutes?

There must be a faster way. Experts would really appreciate if you could shed some light on this.

I don't think there's an approach that's any faster than Deepak's solution.
That said, I don't think Deepak's solution would take much longer than 1 minute. Yes, it takes a while to type a thorough solution on this forum, but on test day, you wouldn't need to write much on your noteboard.

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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cdclark36: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Mon Sep 24, 2012 10:36 am

by cdclark36 » Mon Aug 11, 2014 6:38 am

How can you assume the the passenger takes the first flight leaving at 8:00am?

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[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Mon Aug 11, 2014 6:50 pm

Hi cdclark36,

It's true that you can't assume the passenger would take the 8am flight, but you need a place to "start." To be sure that you have the correct answer, trying doing 2 "tests":

1) What if the passenger started at 8am and took the earliest possible flight at the other airports?
2) What if the passenger started at 9am instead?

With those results side-by-side, what pattern do you notice?

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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j_shreyans: Legendary Member; Posts: 510; Joined: Thu Aug 07, 2014 2:24 amFollowed by: 5 members; Thanked: 3 times

by j_shreyans » Tue Aug 12, 2014 4:50 am

just follow step by step will get the answer.

First 10 min wait at airport B to catch the flight then 55 mins at airport C to catch so the total is

1hr5min

Ans - B[/list][/list]

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shrivats: Junior | Next Rank: 30 Posts; Posts: 23; Joined: Wed Jun 11, 2014 4:28 am; Thanked: 5 times

by shrivats » Wed Aug 13, 2014 8:08 pm

Irrespectively o whether the passenger athes the first flight or not, the answer is not going to change.

flight leaves from a every hour starting 8 am and takes 2 1/2 hours. whatever time the passenger boards, the flight will stand land at B 2 1/2 hours later at half past the hour. ( i.e 10:30, 11:30, 12:30 etc). SO the nect flight at B will always be 10 mins away. And the flight time is 1 hour 10 mins, which means he will always land 50 mins into any hour ( 11:50, 12:50, 13:50 and so on). And flight leaves C every hour again ( 12:45, 13:45 etc).. and the passener has to wait 55 mins.. SO irrespective of whether he takes the 1st flight or not, the answer is the same.

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