The traffic lights at three different road crossings change after every 48 seconds, 72 seconds, and 100 seconds resp. If they change simultaneously at 8 a.m. at what time will they change together again.
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Answer:9am
Step-by-step explanation:
Take lcm of 48,72,100
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If the traffic lights change simultaneously at 8 a.m, then they will change simultaneously again after the LCM of the duration i.e. 48 s, 72 s and 108 s.
LCM of these durations by prime factorisation
48 = 2 × 2 × 2 × 2 × 3 = 2⁴ × 3
72 = 2 × 2 × 2 × 3 × 3 = 2³ × 3²
108 = 2 × 2 × 3 × 3 × 3 = 2² × 3³
LCM of 48, 72 and 108 is 2⁴ × 3³ = 432 seconds.
Hence, They will change after 432 seconds i.e. 7 minutes 12 seconds.
The traffic lights will change after:
8 am + 7 minutes 12 seconds
08 : 07 : 12 am
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