Let's set up a proportion according to the problem: 20 lemons - x rubles; x lemons - 500 rubles.

Thus, $20: x = x: 500$, which means $x^2 = 10000; x = 100$. Two dozen lemons cost 100 rubles, so one dozen costs 50 rubles.

## Answer

50 rubles.
Two dozen lemons cost as many rubles as lemons can be bought for 500 rubles. How much does a dozen lemons cost?

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