Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 18 May 2013, 20:13

# MAry passed a certain gaz station on a highway while

Author Message
TAGS:
Manager
Joined: 23 Mar 2008
Posts: 231
Followers: 1

Kudos [?]: 4 [0], given: 0

MAry passed a certain gaz station on a highway while [#permalink]  07 Jun 2008, 11:51
MAry passed a certain gaz station on a highway while travelling west at a constant speed of 50 miles per hour. Then, 15 minutes later, Paul passed the same gaz station while travelling west at a constant speed of 60 miles per hour. If both drivers maintained their speeds and both remained on the highway for at least 2 hours, how long after he passed the gas station did Paul catch up with MAry?

a) 30 min
b) 45 min
c) 1 hr
d) 1 hr 15 min
e) 1 hr 30 min
Director
Joined: 14 Oct 2007
Posts: 760
Location: Oxford
Schools: Oxford'10
Followers: 11

Kudos [?]: 148 [0], given: 8

Re: drivers [#permalink]  07 Jun 2008, 13:47
--> find the distance that Mary travelled in the 15 mins, d=s.t = 50*.25 = 12.5km

setup this equation

12.5 + 50t = 60t
12.5 = 60t
t = 1.25 (hours) = 1hr 15min

d
SVP
Joined: 28 Dec 2005
Posts: 1612
Followers: 1

Kudos [?]: 53 [0], given: 2

Re: drivers [#permalink]  08 Jun 2008, 06:39
same answer for me, via same method.
Manager
Joined: 23 Mar 2008
Posts: 231
Followers: 1

Kudos [?]: 4 [0], given: 0

Re: drivers [#permalink]  08 Jun 2008, 11:58
OA is D but could you please explain in more details as I didn't get the calculations.
Director
Joined: 14 Oct 2007
Posts: 760
Location: Oxford
Schools: Oxford'10
Followers: 11

Kudos [?]: 148 [1] , given: 8

Re: drivers [#permalink]  08 Jun 2008, 13:12
1
KUDOS
puma wrote:
OA is D but could you please explain in more details as I didn't get the calculations.

sure,

basically, the key to this question is realise that the time that Paul passes Mary, the distance from the gas station will be equal for both drivers.

Key equation here is Speed S = distance/time (s=d/t)

so distance = s*t

So lets deal with Mary first. Distance from the gas station upon being passed d = 50t
For Paul, this distance is the same and contains of two portions. Firstly the static distance Paul is behind when he passes the gas station (15 minutes after Mary.). This distance can be computed by 50*0.25 = 12.5km.

The second portion of Pauls distance is 60t. Total distance bein 12.5 + 60t which equals 50t.

therefore t = 1.25 hours = 1hr 15 min
Manager
Joined: 23 Mar 2008
Posts: 231
Followers: 1

Kudos [?]: 4 [0], given: 0

Re: drivers [#permalink]  09 Jun 2008, 12:28
Why when we calculate the first portion of Paul's distance we multiply 50 by 0.25 and not 60?
Manager
Joined: 08 Jun 2008
Posts: 51
Followers: 0

Kudos [?]: 9 [1] , given: 0

Re: drivers [#permalink]  09 Jun 2008, 12:44
1
KUDOS
I find my way a bit simpler, dunno abt u all

15 minutes later when paul reaches the gas stattion , he is 50/4 miles = 12.5 miles behind
now the difference between speed of 2 cars is 60-50 = 10 miles per hour , which means paul will cover 10 miles in 1 hour so he will cover 12.5 miles in 12.5/10 hour .. hence the answer D

I guess all the explanations look at the same thing from different angles ... I tend to avoid a lot of formula based calculations , stick to the fundamental way of thinking like 12.5 miles to cover , its given paul covers 10 miles of the distance between 2 cars in an hour so how much will he take for 12.5 miles ? simple .. down to the basic
Director
Joined: 14 Oct 2007
Posts: 760
Location: Oxford
Schools: Oxford'10
Followers: 11

Kudos [?]: 148 [0], given: 8

Re: drivers [#permalink]  09 Jun 2008, 12:45
maulikmajithia wrote:
I find my way a bit simpler, dunno abt u all

15 minutes later when paul reaches the gas stattion , he is 50/4 miles = 12.5 miles behind
now the difference between speed of 2 cars is 60-50 = 10 miles per hour , which means paul will cover 10 miles in 1 hour so he will cover 12.5 miles in 12.5/10 hour .. hence the answer D

I guess all the explanations look at the same thing from different angles ... I tend to avoid a lot of formula based calculations , stick to the fundamental way of thinking like 12.5 miles to cover , its given paul covers 10 miles of the distance between 2 cars in an hour so how much will he take for 12.5 miles ? simple .. down to the basic

excellent method, saved two steps on my method!
Kudos
Intern
Joined: 04 May 2008
Posts: 7
Followers: 0

Kudos [?]: 1 [0], given: 0

Re: drivers [#permalink]  09 Jun 2008, 12:46
you can keep this in mind whenever a person or car or watever has travelled for a duration longer than the other person u must add that to your time
for example in this case paul passes the point 15 minutes after mary hence mary has been travelling for 15 mins longer than paul
also the distances they travel are equal becuase paul is going to catch up with mary

so we can set up the foll equations

Mary
Speed 50
Time t+15/50
Distance d

Paul
Speed 60
Time t
Distance d

Hence we get 50(t+1/4)=d and 60t=d
Simplyfying we get 50t+12.5=60t and eventually t=1.25 which is equivalent to 1 hour and 15 mins

Hope that explains it mate
Manager
Joined: 23 Mar 2008
Posts: 231
Followers: 1

Kudos [?]: 4 [0], given: 0

Re: drivers [#permalink]  10 Jun 2008, 12:52
Thanks to all for the explanation
Re: drivers   [#permalink] 10 Jun 2008, 12:52
Similar topics Replies Last post
Similar
Topics:
1 Mary passed a certain gas station on a highway while 6 01 Nov 2007, 11:28
Peter, Paul, and Mary each received a passing score on 9 29 May 2008, 20:35
Mary on the highway 3 01 May 2010, 09:31
1 Peter, Paul, and Mary each received a passing score on 3 17 Jan 2011, 17:09
A certain highway is to be divided into 3 lanes. 1 19 Aug 2012, 09:27
Display posts from previous: Sort by