For every head, there are at least two legs.
Therefore, there are at least 50 legs for 25 heads.
For every cow's head, however, there are still two legs missing then.
Therefore, the remaining legs belong to the cows (2 per cow).
There are 72 - 50 = 22 legs remaining.
These are the remaining legs of 11 cows.
The number of chickens is 25 - 11 = 14.
Conclusion: farmer Axel has bought 11 cows and 14 chickens.
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