Factorization help.

[jaysinhp]

I found my self stuck when I compare my answer with the given answer in the book. Following is the answer.
Question : "On one road three consecutive traffic lights change after 36,42 and 72 seconds respectively. If the lights are first switched on at 9.00 A.M. sharp at what time will they change simultaneously ?"

Options :
(a) 9 : 08 : 04
(b) 9 : 08 : 24
(c) 9 : 08 : 44
(d) None of the above.

I found the the LCM of 36,42,72 which is 504 seconds. So to convert it to minutes it will change after 8.4 ( 504 / 60) minutes. So according to me it should be (a) 9 : 08 : 04 but in book ( "Quantitative aptitude for the CAT by Arun Sharma fourth edition, page number 19,Chapter number : 1, Equation number : 8") it is given (b) 9 : 08 : 24. Can Anyone explain if I am wrong.

 

[srmichael]

I found my self stuck when I compare my answer with the given answer in the book. Following is the answer.
Question : "On one road three consecutive traffic lights change after 36,42 and 72 seconds respectively. If the lights are first switched on at 9.00 A.M. sharp at what time will they change simultaneously ?"

Options :
(a) 9 : 08 : 04
(b) 9 : 08 : 24
(c) 9 : 08 : 44
(d) None of the above.

I found the the LCM of 36,42,72 which is 504 seconds. So to convert it to minutes it will change after 8.4 ( 504 / 60) minutes. So according to me it should be (a) 9 : 08 : 04 but in book ( "Quantitative aptitude for the CAT by Arun Sharma fourth edition, page number 19,Chapter number : 1, Equation number : 8") it is given (b) 9 : 08 : 24. Can Anyone explain if I am wrong.

Piggybacking off of Denis' hint, 8.4 minutes does not mean 8 minutes and 4 seconds. However, I presume the problem maker knew some kids would think that so that is why he had answer A as an option.

 

[Deleted member 4993]

Problem maker was certainly Subhotosh :idea:

Yep ... that's a good problem ... posed by my fellow cricket player Arun ... but I'll take the credit...