Flashing beacons
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Flashing beacons
Three roadside flashing beacons are all switched on at the same time. One flashes every 6 seconds, one every 9 seconds and the third every 12 seconds. How many seconds after being switched on do they flash at the time?
I am aware you could do it like this:
6 second beacon: 6, 12, 18, 24, 30, 36
9 second beacon: 9, 18, 27, 36
12 second beacon: 12, 24, 36
Hence answer 36 seconds.
However, I am sure these questions get much harder so that it is impossible to write it out long-winded like this. I know there is a rule for these types of problems but can't for the life of me remember what it is!
Can anyone help?
I am aware you could do it like this:
6 second beacon: 6, 12, 18, 24, 30, 36
9 second beacon: 9, 18, 27, 36
12 second beacon: 12, 24, 36
Hence answer 36 seconds.
However, I am sure these questions get much harder so that it is impossible to write it out long-winded like this. I know there is a rule for these types of problems but can't for the life of me remember what it is!
Can anyone help?
Re: Flashing beacons
You want the smallest number that all of these numbers divide into. You could do it by factorizing:Here we go again wrote:Three roadside flashing beacons are all switched on at the same time. One flashes every 6 seconds, one every 9 seconds and the third every 12 seconds. How many seconds after being switched on do they flash at the time?
I am aware you could do it like this:
6 second beacon: 6, 12, 18, 24, 30, 36
9 second beacon: 9, 18, 27, 36
12 second beacon: 12, 24, 36
Hence answer 36 seconds.
However, I am sure these questions get much harder so that it is impossible to write it out long-winded like this. I know there is a rule for these types of problems but can't for the life of me remember what it is!
6 = 2x3
9 = 3x3
12 = 2x2x3
so a common multiple must have all these factors:
2x2x3x3 = 36
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- Posts: 13
- Joined: Thu Jun 05, 2008 10:20 am
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- Posts: 13
- Joined: Thu Jun 05, 2008 10:20 am
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Re: Flashing beacons
can someone please explain how to explain this question to 10 yo? thank you