You've seen this puzzle: a cow changing hands, sums of money adding up and subtracting… and in the end, your mind goes blank. You think you've got the solution, then a detail sows doubt. What if, instead of relying on intuition, we applied a truly reliable method? Spoiler alert: no need to be a math whiz, just follow the steps like you would line up your groceries at the supermarket…
Why this problem confuses us
The trap with this kind of puzzle is confusing two things: money going out (purchases) and money coming in (sales). Our brains tend to remember large numbers and end up rounding or combining the data in their own way . As a result, we think the second operation cancels out the first, or that we should add all the amounts together. Wrong! Each buy-and-sell transaction is a mini-story with its own beginning and end.
Quick reminder: profit, expense, and cash flow
To stay calm , we use the basic trick: profit is what comes in minus what goes out over a complete sequence. In other words, we never calculate a gain at the time of purchase (which is an expense), but at the time of sale (which confirms the value). Like at a yard sale: as long as the item isn't resold, the gain doesn't really exist.
Step by step: unraveling the cow mystery
We follow the thread, calmly:
- You buy the cow for €800. At this stage, there is no profit, just an outflow of money.
- You sell it for €1,000. This first “buy + sell” sequence results in: €1,000 – €800 = +€200.
- You buy it back for €1,100. Again, this is just an expense; no gain at this precise moment.
- You resell it for €1,300. Second complete sequence: 1,300 – 1,100 = +€200.
Add up the profits from the complete sequences (and only those): €200 + €200 = €400. Yes, that's all! We don't mix purchases from different sequences, we don't average prices , we respect the natural order: each sale validates the profitability of the previous purchase.
The classic trap to avoid
Many people think that buying back tickets for €1,100 "eats up" the initial €200 profit. In reality, it simply starts a new transaction. Imagine two consecutive train tickets: one cost you €800 and earned you €1,000, the other cost you €1,100 and earned you €1,300. Each trip has its own profitability; you don't combine the tickets to recalculate the overall itinerary. The moral of the story: think in complete "buy → sell" blocks.
A handy tip to avoid making mistakes
When a problem involves multiple money transactions, draw two columns on a corner of the sheet of paper: Outflows (purchases) and Inflows (sales). Then group the transactions into logical pairs. Here:
Sequence 1: entry €1,000 – exit €800 = +€200.
Sequence 2: entry €1,300 – exit €1,100 = +€200.
Next, add up the profits from the sequences: +€400 in total. It's as simple as whipping egg whites: step by step, without rushing.
In short, with figures and clear details
First transaction: €800 → €1,000 = +€200.
Second transaction: €1,100 → €1,300 = +€200.
Total profit: €400.
Keep this method handy: as soon as the numbers get tangled up, break the story down into small scenes… and the solution will emerge quite naturally!
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