Answer:
The time period after which the traffic lights at three different road crossing changes simultaneously again will be the LCM of 48, 72 and 108. R 48, 36, 54 2 24, 36, 54 2 12, 18, 27 2 6, 9, 27 3 3, 9, 27 3 1, 3, 9 3 1, 1, 3 1, 1, 1
\[\therefore \] LCM \[=2\times 2\times 2\times 2\times 3\times 3\times 3=432\] \[=\frac{432}{60}\min =7\]minute 12 second \[\left[ \begin{align} & \because 1\min \,=60 \\ & \text{and1s=}\frac{1}{60}\min \\ \end{align} \right]\] So, time when they will change again \[\begin{matrix} = & \begin{align} & 07:00:00 \\ & \frac{+\,\,\,\,\,\,07:12}{07:07:12} \\ \end{align} \\ \end{matrix}\] i.e. 7 min 12 s past 7 a.m.
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