You’ve seen this riddle: a cow changing hands, sums of money adding up and subtracting… and in the end, your mind gets confused. You think you have the solution, then a detail sows doubt. What if, instead of trusting intuition, you applied a truly reliable method? Spoiler: no need to be a mathematician, just line up the steps like you line up your products in the supermarket…
Why this problem confuses us
The trap with this kind of puzzle is that it confuses two things: money going out (purchases) and money coming in (sales). Our brain mostly remembers the big numbers and ends up “rounding” or combining the data in its own way . As a result, we believe that the second operation cancels out the first, or that we have to add up all the amounts in a block. Wrong! Each purchase and resale is a mini-story with its own beginning and end.
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