The question is:
''On the coast there are three lighthouses.
'The first light shines for 3 seconds then it is off for three seconds. The second light shines for 4 seconds then it is off for 4 seconds. The third light shines for 5 seconds then it is off for 5 seconds. All three lights have just come on together.
a) 'When is the first time that all three of the lights will be off together?
b) 'When is the next time that all three lights will come on at exactly the same moment?'
I solved the problems with a simple chart on a grid, in about 30 seconds; I prefer visual solutions. However, there must be a mathematical solution (presumably relating to factors), and I am assuming that the children to whom the homework was presented, covered this is in their lessons (although, that may not be the case)! Can anyone advise the mathematical solution?
The article that I read (on MSN) is not well-written; perhaps one of the 8 year-olds wrote it, and no mathematical answer has been provided (at least, not a correct one that I can find)!
Below is a link to the article on MSN; there is no link to the original Mumsnet article, and I suspect that the MSN article was syndicated from elsewhere:
https://www.msn.com/en-au/lifestyle/sma ... ar-AAxdLD3