Question

D. The traffic lights at different road-crossings change after every 60 seconds, 72 seconds and
seconds respectively. If they change simultaneously at 9 a.m., how many times will they chang
simultaneously in between 9 a.m. and 10 a.m.?​

Answer 1

Answer:

changing time me 2 periods hu diye hai aur 3rd wala nhi hai.....

Step-by-step explanation:

so that it can't be solve without 3rd value

Answer 2

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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