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# On a track for remote controlled racing cars

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Intern
Joined: 08 Oct 2016
Posts: 12
On a track for remote controlled racing cars  [#permalink]

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14 Nov 2016, 07:34
14
00:00

Difficulty:

45% (medium)

Question Stats:

67% (01:49) correct 33% (02:06) wrong based on 289 sessions

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On a track for remote controlled racing cars, racing car A completes the track in 55 seconds, while racing car B completes it in 35 seconds. If they both start at the same time after how many seconds will they be side by side again.

A. 275
B. 325
C. 385
D. 425
E. None of these
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Status: QA & VA Forum Moderator
Joined: 11 Jun 2011
Posts: 4469
Location: India
GPA: 3.5
Re: On a track for remote controlled racing cars  [#permalink]

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14 Nov 2016, 12:11
3
2
voccubd wrote:
Abhishek009 wrote:
voccubd wrote:
On a track for remote controlled racing cars, racing car A completes the track in 55 seconds, while racing car B completes it in 35 seconds. If they both start at the same time after how many seconds will they be side by side again.

A. 275
B. 325
C. 385
D. 425
E. None of these

Time required in seconds will be LCM ( 35, 55 ) = 385

Hence, answer will be (C) 385

Sorry I can't understand. Can you please explain in details or suggest me any resource material on this ? I found another similar problem in the internet where L.C.M wasn't the answer.

Cumulative lap timings of Car A and Car B is as follows -

Car A = { 55 , 110 , 165 , 220 , 275 , 330 , 385 , 440..........}

Car B = { 35, 70, 105 , 140 , 175 , 210 , 245 , 280 , 315 , 350 , 385, 420........}

Since, both are independent events, they will start again at 385 seconds ( from starting ) , hence, LCM is preferred here..
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Abhishek....

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Board of Directors
Status: QA & VA Forum Moderator
Joined: 11 Jun 2011
Posts: 4469
Location: India
GPA: 3.5
Re: On a track for remote controlled racing cars  [#permalink]

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14 Nov 2016, 11:14
1
voccubd wrote:
On a track for remote controlled racing cars, racing car A completes the track in 55 seconds, while racing car B completes it in 35 seconds. If they both start at the same time after how many seconds will they be side by side again.

A. 275
B. 325
C. 385
D. 425
E. None of these

Time required in seconds will be LCM ( 35, 55 ) = 385

Hence, answer will be (C) 385

_________________
Thanks and Regards

Abhishek....

PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS

How to use Search Function in GMAT Club | Rules for Posting in QA forum | Writing Mathematical Formulas |Rules for Posting in VA forum | Request Expert's Reply ( VA Forum Only )
Intern
Joined: 08 Oct 2016
Posts: 12
Re: On a track for remote controlled racing cars  [#permalink]

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14 Nov 2016, 12:02
Abhishek009 wrote:
voccubd wrote:
On a track for remote controlled racing cars, racing car A completes the track in 55 seconds, while racing car B completes it in 35 seconds. If they both start at the same time after how many seconds will they be side by side again.

A. 275
B. 325
C. 385
D. 425
E. None of these

Time required in seconds will be LCM ( 35, 55 ) = 385

Hence, answer will be (C) 385

Sorry I can't understand. Can you please explain in details or suggest me any resource material on this ? I found another similar problem in the internet where L.C.M wasn't the answer.
VP
Joined: 07 Dec 2014
Posts: 1189
Re: On a track for remote controlled racing cars  [#permalink]

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14 Nov 2016, 20:06
1
voccubd wrote:
On a track for remote controlled racing cars, racing car A completes the track in 55 seconds, while racing car B completes it in 35 seconds. If they both start at the same time after how many seconds will they be side by side again.

A. 275
B. 325
C. 385
D. 425
E. None of these

55=11*5
35=7*5
lcm=11*7*5=385
Director
Joined: 05 Mar 2015
Posts: 998
Re: On a track for remote controlled racing cars  [#permalink]

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28 Nov 2016, 05:10
gracie wrote:
voccubd wrote:
On a track for remote controlled racing cars, racing car A completes the track in 55 seconds, while racing car B completes it in 35 seconds. If they both start at the same time after how many seconds will they be side by side again.

A. 275
B. 325
C. 385
D. 425
E. None of these

55=11*5
35=7*5
lcm=11*7*5=385

Bunuel/Experts

What will be the approach if question mentions that Car b started 10 minuter after Car A??

THanks
Rohit
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Location: United States (TX)
Concentration: Finance, Marketing
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On a track for remote controlled racing cars  [#permalink]

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26 Sep 2017, 17:38
1
rohit8865 wrote:
gracie wrote:
voccubd wrote:
On a track for remote controlled racing cars, racing car A completes the track in 55 seconds, while racing car B completes it in 35 seconds. If they both start at the same time after how many seconds will they be side by side again.

A. 275
B. 325
C. 385
D. 425
E. None of these

55=11*5
35=7*5
lcm=11*7*5=385

Bunuel/Experts

What will be the approach if question mentions that Car b started 10 minuter after Car A??

THanks
Rohit

rohit8865 - I am no expert but here is my dig on it.

Speed of Car A = 1/35
Speed of Car B = 1/55

Convert 10 minutes to seconds. That will be 600 secs

Distance traveled by Car A in 600 secs = 600/55 = 120/11 laps.

Relative speed = $$\frac{1}{35}-\frac{1}{55}$$ [subtract slower from faster because they are traveling in the same direction]
So, Relative speed = $$\frac{4}{385}$$

Relative distance = 120/11 laps.

Time when they meet = $$\frac{\frac{120}{11}}{\frac{4}{385}}$$ = 1050 secs or 17.5 mins.

Hope I am correct
Manager
Joined: 24 Jun 2017
Posts: 121
Re: On a track for remote controlled racing cars  [#permalink]

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26 Sep 2017, 19:41
55x=35y (point in time when they run side by side)
x=35y/55 (integer, seconds)

x= 7*5*y/5*11, then y = 11, so 385
you can read it as in 385 secs car A(x) will 7 complete tracks and car B 11
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9218
Location: Pune, India
Re: On a track for remote controlled racing cars  [#permalink]

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23 Oct 2018, 04:59
1
voccubd wrote:
On a track for remote controlled racing cars, racing car A completes the track in 55 seconds, while racing car B completes it in 35 seconds. If they both start at the same time after how many seconds will they be side by side again.

A. 275
B. 325
C. 385
D. 425
E. None of these

They will be side-by-side again when the faster car covers exactly one circle more than the slower car. Assuming the track length to be 35*11 meters, speed of car A is 7 m/sec and speed of car B is 11 meters/sec. Car B will cover the extra 35*11 meters (one full circle) in 35*11/4 secs = 96.25 secs

The problem is different when you have to find the time when they meet up again at the starting point.

Car A is at the starting point after: 55 sec, 110 sec, 165 sec, 220 sec ... etc
Car B is at the starting point after: 35 sec, 70 sec, 105 sec, 140 sec ... etc
So we need to take LCM here. The time when both would be at the starting point: 35*11 = 385 secs

Since the question has only 385 as an option, it must specify side by side at the starting point.
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Karishma
Veritas Prep GMAT Instructor

Re: On a track for remote controlled racing cars   [#permalink] 23 Oct 2018, 04:59
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