Question:
A red light flashes three times per minute and a green light flashes five times in 2 min at regular intervals. If both lights start flashing at the same time, how many times do they flash together in each hour?
A red light flashes three times per minute and a green light flashes five times in 2 min at regular intervals. If both lights start flashing at the same time, how many times do they flash together in each hour?
Show Hint
Convert both flash rates into the gap between two flashes in seconds, then take the LCM of the two gaps.
Updated On: Nov 4, 2026
- 20
- 24
- 30
- 60
Show Solution
Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Step 1: Find the gaps between flashes:
Red: 3 flashes per minute, so one flash every \(60/3 = 20\) seconds.
Green: 5 flashes in 2 minutes, so one flash every \(120/5 = 24\) seconds.
Step 2: When do they flash together?
They coincide every \(\text{LCM}(20, 24) = 120\) seconds, that is every 2 minutes.
Step 3: Count in one hour:
One hour = 3600 seconds, so the number of times they flash together is \(3600/120 = 30\).
Final Answer:
The correct option is (3): 30
Red: 3 flashes per minute, so one flash every \(60/3 = 20\) seconds.
Green: 5 flashes in 2 minutes, so one flash every \(120/5 = 24\) seconds.
Step 2: When do they flash together?
They coincide every \(\text{LCM}(20, 24) = 120\) seconds, that is every 2 minutes.
Step 3: Count in one hour:
One hour = 3600 seconds, so the number of times they flash together is \(3600/120 = 30\).
Final Answer:
The correct option is (3): 30
Was this answer helpful?
0
0
Top CAT Quantitative Aptitude Questions
- In a triangle ABC,AB=AC=8cm. A circle drawn with BC as diameter passes through A. Another circle drawn with center at A passes through B and C. Then the area,in sq.cm,of the overlapping region between the two circles is
- The simple interest accrued on an amount of Rs.25,000 at the end of three years is Rs.7,500. What would be the compound interest accrued on the same amount at the same rate in the same period?
- What is the sum of all roots of the equation \(|x+4|^2–10|x+4|=24\)?
- A solid metal sphere is melted and smaller spheres of equal radii are formed. 10% of the volume of the sphere is lost in the process. The smaller spheres have a radius which is \(\frac{1}{9}\text{th}\) the larger sphere. If 10 litres of paint were needed to paint the larger sphere,how many litres are needed to paint all the smaller spheres?
- The ratio of the ages of a husband and his wife when they got married was 6:5. 4 years and 6 years after their marriage they had their 1st and 2nd children. The sum of the present ages of the husband and wife is 6.4 times the sum of the present ages of their children. The average age of the family at present is 18.5 years. Find the ratio of the ages of the husband and wife when their second child was born.
View More Questions
Top CAT Arithmetic Questions
- Once I had been to the post office to buy five-rupee, two-rupee and one-rupee stamps. I paid the clerk Rs. 20, and since he had no change, he gave me three more one-rupee stamps. If the number of stamps of each type that I had ordered initially was more than one, what was the total number of stamps that I had when I left the post office?
Four sisters - Suvarna, Tara, Uma and Vibha - are playing a game such that the loser doubles the money of each of the other players from her share. They played four games and each sister lost one game, in alphabetical order. At the end of the fourth game, each sister had Rs. 32.
- 72 hens cost Rs.\ ____ 96.7____. Then what does each hen cost, where two digits in place of ‘____’ are not visible or are written in illegible hand?
- A person who has a certain amount with him goes to market. He can buy 50 oranges or 40 mangoes. He retains 10% of the amount for taxi fares and buys 20 mangoes, and of the balance he purchases oranges. Number of oranges he can purchase is
- A man invests Rs.\ 3,000 at the rate of 5% per annum. How much more should he invest at the rate of 8%, so that he can earn a total of 6% per annum?
View More Questions
Top CAT Questions
- Compare and contrast between Portia and Jessica characters in Merchant of Venice.
- In a triangle ABC,AB=AC=8cm. A circle drawn with BC as diameter passes through A. Another circle drawn with center at A passes through B and C. Then the area,in sq.cm,of the overlapping region between the two circles is
- The simple interest accrued on an amount of Rs.25,000 at the end of three years is Rs.7,500. What would be the compound interest accrued on the same amount at the same rate in the same period?
- What is the sum of all roots of the equation \(|x+4|^2–10|x+4|=24\)?
- A solid metal sphere is melted and smaller spheres of equal radii are formed. 10% of the volume of the sphere is lost in the process. The smaller spheres have a radius which is \(\frac{1}{9}\text{th}\) the larger sphere. If 10 litres of paint were needed to paint the larger sphere,how many litres are needed to paint all the smaller spheres?
View More Questions