MGMAT TIME SPEED DIST

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anksbhandari: Junior | Next Rank: 30 Posts; Posts: 26; Joined: Wed Apr 30, 2008 11:05 am; Location: India

by anksbhandari » Sat Aug 02, 2008 9:28 am

Tom and Linda stand at point A. Linda begins to walk in a straight line away from Tom at a constant rate of 2 miles per hour. One hour later, Tom begins to jog in a straight line in the exact opposite direction at a constant rate of 6 miles per hour. If both Tom and Linda travel indefinitely, what is the positive difference, in minutes, between the amount of time it takes Tom to cover half of the distance that Linda has covered and the amount of time it takes Tom to cover twice the distance that Linda has covered?

a. 60
b. 72
c. 84
d. 90
e. 108

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Source: Beat The GMAT — Problem Solving | Sat Aug 02, 2008 9:28 am

pepeprepa: Legendary Member; Posts: 661; Joined: Tue Jul 08, 2008 12:58 pm; Location: France; Thanked: 48 times

by pepeprepa » Sat Aug 02, 2008 10:09 am

Would say E

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eccentric: Senior | Next Rank: 100 Posts; Posts: 88; Joined: Tue Jul 15, 2008 1:43 amFollowed by: 1 member; Thanked: 3 times; GMAT Score:590

by eccentric » Sat Aug 02, 2008 11:31 am

Distance covered by Linda in a min = 1/30
Distance covered by Tom in a min = 1/10

In 120 mins tom would be exactly 2 times the distance covered by Linda.
while he starts an hour later by that time Linda would have covered 2miles now it takes 12 minutes for Tom to reach 1.2 miles which is exactly 1/2 the distance covered by linda in the same time.
hence 120-12 = 108 is correct choice...

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egybs: Master | Next Rank: 500 Posts; Posts: 178; Joined: Wed May 14, 2008 3:51 pmFollowed by: 1 member; Thanked: 16 times; GMAT Score:99%+

Re: MGMAT TIME SPEED DIST

by egybs » Sat Aug 02, 2008 11:32 am

We know Linda has already traveled 2 miles before things really get going:

(2+2t)(1/2) = 6t
1+t = 6t
t =1/5 = 12 min

(2+2t)(2) = 6t
4+4t = 6t
2t = 4
t =2 or 120 minutes

120 min - 12 min = 108 min.

E

anksbhandari wrote:Tom and Linda stand at point A. Linda begins to walk in a straight line away from Tom at a constant rate of 2 miles per hour. One hour later, Tom begins to jog in a straight line in the exact opposite direction at a constant rate of 6 miles per hour. If both Tom and Linda travel indefinitely, what is the positive difference, in minutes, between the amount of time it takes Tom to cover half of the distance that Linda has covered and the amount of time it takes Tom to cover twice the distance that Linda has covered?

a. 60
b. 72
c. 84
d. 90
e. 108

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sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Sat Aug 02, 2008 9:24 pm

Hi understood the 120 minutes .. but can someone explain me the 12 mints ?

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beeparoo: Master | Next Rank: 500 Posts; Posts: 200; Joined: Sun Jun 17, 2007 10:46 am; Location: Canada; Thanked: 9 times

Re: MGMAT TIME SPEED DIST

by beeparoo » Mon Aug 04, 2008 10:02 am

egybs wrote:We know Linda has already traveled 2 miles before things really get going:

(2+2t)(1/2) = 6t
1+t = 6t
t =1/5 = 12 min

(2+2t)(2) = 6t
4+4t = 6t
2t = 4
t =2 or 120 minutes

120 min - 12 min = 108 min.

E

anksbhandari wrote:Tom and Linda stand at point A. Linda begins to walk in a straight line away from Tom at a constant rate of 2 miles per hour. One hour later, Tom begins to jog in a straight line in the exact opposite direction at a constant rate of 6 miles per hour. If both Tom and Linda travel indefinitely, what is the positive difference, in minutes, between the amount of time it takes Tom to cover half of the distance that Linda has covered and the amount of time it takes Tom to cover twice the distance that Linda has covered?

a. 60
b. 72
c. 84
d. 90
e. 108

@ sudhir3127: If you understood the set up of equations that egybs used, especially for that which resulted in 120 minutes, how do you have trouble understanding the set up which resulted in 12 minutes?
They are the same logic.

(2+2t)(1/2) = 6t <---Here (1/2)Distance of Linda = Distance of Tom
1+t = 6t
t =1/5 = 12 min <--- Here, Time(of Tom) = 1/5 hr*(60 min/hr) = 12 min

GMAT obsession begone - girl needs her social life back.

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