Lighthouses And How They Work
lighthouses and how they work
Maths Question Help?! BEST ANSWER=10 POINTS!?
Help is needed! I've got a test on the higher paper in exactly 2 weeks time and I'm revising. At the moment I'm on Factors and Multiples, and I've come across this question and remembered how I lost marks on questions like these.
A lighthouse flashes every 56 seconds.
Another lighthouse flashes every 40 seconds.
At 9 p.m they both flash at the same time.
What time will it be when they next both flash at the same time?
Right, I've worked out the HCF and LCM:
HCF= 8
LCM= 280
But thats pretty much all I know since this question is based on this topic.
What gets to me is, how can they both flash at the same time?! It may seem like a stupid question but...nevermind.
Please do explain! I know this is very easy for most of you guys! Thank you!!
HCF= Highest Common Factor
LCM= Lowest Common Multiple
This depends on the assumption that the "flash" actually occurs in no time at all (otherwise you have to add the duration of the "flash" to the calculation and it then gets horribly complicated) . The LCM is the smallest number that both intervals between flashing will divide into exactly (by definition). Therefore the flashings are synchronised every 280 seconds, so if they both happened together at 9 pm (21:00) they will next flash together at 9pm plus 280 seconds. 280 seconds is 4 minutes and 40 seconds, so the next simultaneous flashing will occur at 21:04:40.
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