GCSE Secondary Maths Age 13-17 - Number: LCM and HCF - Explained

The video tutorial explains a problem involving three lamps that flash at different intervals. The task is to determine how many times the lamps flash simultaneously in one hour. The solution involves finding the lowest common multiple (LCM) of the intervals, which is 360 seconds. This means the lamps flash together every 6 minutes, resulting in 10 flashes in an hour. The tutorial also discusses the marking scheme and the possibility of an alternative answer if the first flash is considered at time zero.

What is the main problem discussed in the video regarding the three lamps?

• How to make the lamps flash at different times

• How to turn off the lamps simultaneously

• How to find when the lamps flash together

• How to change the color of the lamps

What is the lowest common multiple (LCM) of the intervals 20, 45, and 120 seconds?

• 600 seconds

• 240 seconds

• 360 seconds

• 480 seconds

After how many minutes do the lamps first flash together?

• 10 minutes

• 3 minutes

• 5 minutes

• 6 minutes

How many times do the lamps flash together in one hour if the first flash is at t=0?

• 9 times

• 10 times

• 11 times

• 12 times

What are the marks awarded for in the question discussed?

• Calculating the time, finding the LCM, and the final answer

• Finding the LCM, calculating the distance, and the final answer

• Calculating the speed of light, finding the LCM, and the final answer

• Finding the LCM, calculating the first flash, and the final answer