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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?
  • a)
    30
  • b)
    24
  • c)
    20
  • d)
    60
  • e)
    32
Correct answer is option 'A'. Can you explain this answer?
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Verified Answer
A red light flashes 3 times per minute and a green light flashes 5 tim...
The red light flashes once in 60/3 = 20 seconds 
and the green light flashes once in 120/5 = 24 seconds
If both start flashing at the same time, they flash simultaneously for the first time after a number of seconds
that is the LCM of 20 and 24, is 120.
If the lights flash simultaneously every 120 seconds, they flash together every 2 minutes.
They therefore flash simultaneously for 60/2 = 30 times each hour.
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Most Upvoted Answer
A red light flashes 3 times per minute and a green light flashes 5 tim...
To find the number of times the red light and green light flash together in each hour, we need to determine the least common multiple (LCM) of the two flash rates.

The red light flashes 3 times per minute. We can represent this as 3 flashes per minute or 3 flashes/minute.

The green light flashes 5 times in two minutes. We can represent this as 5 flashes in 2 minutes or 5 flashes/2 minutes.

Now, we need to convert both rates to a common denominator. The LCM of 1 minute and 2 minutes is 2 minutes. So, let's convert both rates to flashes/2 minutes.

For the red light:
3 flashes/minute * (2 minutes/2 minutes) = 6 flashes/2 minutes

For the green light:
5 flashes/2 minutes * (1 minute/1 minute) = 5 flashes/2 minutes

Now that we have both rates in flashes/2 minutes, we can find the LCM.

The LCM of 6 and 5 is 30. This means that the red light and green light will flash together every 30 flashes/2 minutes.

To find the number of times they flash together in each hour, we need to convert hours to minutes. There are 60 minutes in an hour.

Now, let's calculate the number of times they flash together in each hour:

Number of times they flash together in each hour = (Number of minutes in an hour) / (Time for them to flash together)

= (60 minutes) / (30 flashes/2 minutes)

= (60 minutes) / (15 flashes/minute) [Since 30 flashes/2 minutes = 15 flashes/minute]

= 4 flashes/minute

Therefore, the red light and green light will flash together 4 times in each minute.

Number of times they flash together in each hour = (Number of minutes in an hour) * (Number of times they flash together in each minute)

= (60 minutes) * (4 flashes/minute)

= 240 flashes

Hence, the correct answer is option 'A', 30 flashes.
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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?a)30b)24c)20d)60e)32Correct answer is option 'A'. Can you explain this answer?
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