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On a track for remote controlled racing cars

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On a track for remote controlled racing cars  [#permalink]

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New post 14 Nov 2016, 06:34
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  45% (medium)

Question Stats:

69% (01:29) correct 31% (01:47) wrong based on 272 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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Re: On a track for remote controlled racing cars  [#permalink]

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New post 14 Nov 2016, 11:11
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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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Re: On a track for remote controlled racing cars  [#permalink]

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New post 14 Nov 2016, 10:14
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

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Thanks and Regards

Abhishek....

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

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Re: On a track for remote controlled racing cars  [#permalink]

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New post 14 Nov 2016, 11:02
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.
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Re: On a track for remote controlled racing cars  [#permalink]

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New post 14 Nov 2016, 19:06
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
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Re: On a track for remote controlled racing cars  [#permalink]

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New post 28 Nov 2016, 04:10
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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On a track for remote controlled racing cars  [#permalink]

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New post 26 Sep 2017, 16:38
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 :)
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Re: On a track for remote controlled racing cars  [#permalink]

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New post 26 Sep 2017, 18:41
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
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Re: On a track for remote controlled racing cars  [#permalink]

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New post 23 Oct 2018, 03:59
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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Re: On a track for remote controlled racing cars &nbs [#permalink] 23 Oct 2018, 03:59
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