I have this math question today that I am puzzled by. It is based off of “1998, a 17-year brood and a 13-year brood both emerged in Missouri.”, however the question is “How many years will pass before they emerge together again?”. Now I know that if I write out the numbers, starting from 1998, and add seventeen I will get a list of possibilities and then if I do the same with thirteen I can compare the two lists of numbers. HOWEVER, is there an easier way to do this? A formula of some sort that can cut the work down?
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If you multiply 17 times 77 (the magic number) and then you do the same for 13, you'll get 1309 and 1001. You then set it up as a fraction 1309 / 1001 and multiply that by 40/1. You then round down and get 52 for your answer. I use this method all the time... Learned it in 7th grade!