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  • The traffic lights at three different road crossings change after every 48 seconds 72 seconds and 108 seconds respectively If they change simultaneously at 7 a m at what time will they change simultaneously again

6. The traffic lights at three different road crossings change after every 48 seconds, 72 seconds and 108 seconds respectively. If they change simultaneously at 7 a.m., at what time will they change simultaneously again?

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The time period after which these lights will change = LCM of 48, 72 and 108

\begin{array}{|c|c|}\hline 2 & {48,72,108} \\ \hline 2 & {24,36,54} \\ \hline 2 & {12,18,27} \\ \hline 2 & {6,9,27} \\ \hline 3 & {1,3,9} \\ \hline 3 & {1,1,3} \\ \hline 3 & {1,1,1} \\ \hline\end{array}

LCM=2 \times 2 \times 2 \times 2 \times 3 \times 3 \times 3 = 432

They will change together after every 432 seconds i.e., 7 min 12 seconds.

Hence, they will change simultaneously at 7:07:12 am.

Posted by

Pankaj Sanodiya

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