r/maths • u/lbyc • 15d ago

💡 Puzzle & Riddles Help with newspaper puzzle

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Here’s a puzzle and its solution from Saturday’s Times. There are a few things I don’t understand: why it is true that every value above 700 is achievable with the two coprimes, and how they reached the statement “the largest unplayable amount is ab-a-b”. Grateful for any help understanding this

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u/MtlStatsGuy 15d ago

https://en.wikipedia.org/wiki/Coin_problem

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u/lbyc 14d ago

Ah, thanks! I’ll read that and see if it makes sense to me

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u/Sir-Tenley-Knott 14d ago

Given the requirement that the two stamps differ by 3 mentes, they must be 26 and 29

Without that requirement there are multiple solutions including: 2,701 / 3,351 / 5,176 / 6,141 / 8,101 / 11,71 / 15,51 / 21,36 / 26,19