) In a circular race track of length 100 m, three persons A, B and C start together. A and B start in the same direction at speeds of 10 m/s and 8 m/s respectively. While C runs in the opposite at 15 m/s. When will all the three meet for the first time on the after the start? a) After 4 s b) After 50 s c) After 100 s d) After 200 s

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Questions by nurankl84   answers by nurankl84

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chetan pande

  • Aug 2nd, 2006
 

In such type of questions get ur answers from options itself..

take 1st option and calculate distance travelled by each person so it will be (4*10)=40m for A,(4*8)=32,(4*15)=60............so here distance travelled by each person is not a Multiple of 100 .....

likewise try for other options ................

The correct answer is 100s

Basheer

  • Aug 5th, 2006
 

Yes it is           C) after 100s

In 100 sec A completes 10 cycles.

                B completes 8 cycles.

                C completes 15 cycles.

D) after 200 sec also, all the three will be at same place but this is not the first time.

rajesh0457

  • Jul 15th, 2008
 

 
 A takes (100m) / (10m/s) = 10s to finish one complte round.

 B takes (100m) / (8m/s) = 12.5s to finish one complte round.

 C takes (100m) / (15m/s) = (20/3)s to finish one complte round.

For them to meet, the time will be LCM of above three times

  ie LCM(10,12.5,20/3)=

                                 = LCM(10/1,25/2,20/3)
                                 = LCM(10,25,20)/GCD(1,2,3)
                                 = 50/1
                                 = 50 seconds.

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manoj21988

  • Aug 5th, 2008
 

Here considering the same direction they meet for the first time when A overtakes B as well as A overtakes C simultaneously for the first time

Thus, A overtakes B every 50 seconds

A overtakes C every 4 seconds (100/25)
LCM is 100 seconds
After 100 seconds, A travels 1000m(reaches start point), B 800m(start pt), C 1500m(aftr 15 rounds reaches start pt again)
Thus its 100s at the start

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Arnab Das

  • Jun 29th, 2021
 

LCM(10, 25, 20) is 100, NOT 50

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