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CAT 2001 | Question: 5

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A red light flashes $3$ times per minute and a green light flashes $5$ times in two minutes at regular intervals. If both lights start flashing at the same time, how many times do they flash together in each hour?

  1. $30$
  2. $24$
  3. $20$
  4. $60$
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Red light flashes 3 times per min (once every 20 sec)

Green light flashes 5 times per 2 min (once every 24 sec)

 

For flash together together=LCM of (20 & 24) => together once every 120 sec

No. of flashes in each hour =$\frac{3600}{120}=30$

 

Hence,option (1)30.

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