7. The donkey had to share the feed (oats and hay) with both the horse and the cow.
1) If the donkey eats oats, then the horse eats the same as the cow.
2) If the horse eats oats, then the donkey eats what the cow does not eat.
3) If the cow eats hay, then the donkey eats the same as the horse.

Who always eats from the same feed trough?
7. The problem is about three animals - a donkey, a horse, and a cow, which ate oats and hay. Let's draw a table reflecting all possible combinations of the animals eating oats (O) and hay (S).

|  | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| :--- | :--- | :--- | :--- | :--- | :--- | :--- | :--- | :--- |
| Donkey | O | O | O | O | S | S | S | S |
| Horse | O | O | S | S | O | O | S | S |
| Cow | O | S | O | S | O | S | O | S |

From the first condition, if the donkey eats oats, then the horse eats the same as the cow. Therefore, we exclude options 2 and 3.

|  | 1 | 4 | 5 | 6 | 7 | 8 |
| :--- | :--- | :--- | :--- | :--- | :--- | :--- |
| Donkey | O | O | S | S | S | S |
| Horse | O | S | O | O | S | S |
| Cow | O | S | O | S | O | S |

According to the second condition, if the horse eats oats, then the donkey eats what the cow does not eat. This condition excludes options 1 and 6.

|  | 4 | 5 | 7 | 8 |
| :--- | :--- | :--- | :--- | :--- |
| Donkey | O | S | S | S |
| Horse | S | O | S | S |
| Cow | S | O | O | S |

The third condition states: if the cow eats hay, then the donkey eats the same as the horse. This allows us to exclude the fourth option.

|  | 5 | 7 | 8 |
| :--- | :--- | :--- | :--- |
| Donkey | S | S | S |
| Horse | O | S | S |
| Cow | O | O | S |

Thus, we are left with the 5th, 7th, and 8th options, which do not contradict all three conditions. From these, it follows that only the donkey eats from the hay feeder.

Answer: The donkey always eats from the hay feeder.

## NINTH