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I think where people get into trouble with fractions and especially where money is concerned, is in not realizing that lowering an expense by 1/4 means that the same money lasts 1/3 longer.

I can't count the number of times I've had to explain to someone, especially in project roadmap discussions, that ±20% doesn't cancel out. 1.2 x 0.8 != 1.0. ±5% almost does, and people extrapolate to larger numbers and make strategy based on it.



There is a fairground/fundraising con based on this.

Customer gives you one or two dollars. You set up a card to keep track of a set number of coin flips - 10 say.

The deal/catch: - heads = multiply their money by 1.25. - tails = multiply their money by 0.78.

People will usually see +0.25 payout vs -0.22 cost instead of the actual fractional payout as you've already noted.

The nice thing, is one person flips a coin and is the crowd pleaser, while another is the note taker. People can join at any time.




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