A magpie cooked porridge and fed her chicks. The third chick received as much porridge as the first two combined. The fourth one received as much as the second and third. The fifth one received as much as the third and fourth. The sixth one received as much as the fourth and fifth. The seventh one did not get any - the porridge ran out! It is known that the fifth chick received 10 grams of porridge. How much porridge did the magpie cook?

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Replacing the first two chicks with the third, and the sixth with the fifth and fourth, we see that the total amount of porridge is twice as much as what the third, fourth, and fifth chicks received. But this is four times more than what the fifth chick received, so the magpie cooked $10 \cdot 4=40$ g of porridge.

## Answer

40 g.

In the cells of a $3 \times 3$ square, letters are written (see figure). Can they be rearranged so that any two letters that were initially a knight's move apart end up a king's move apart after the rearrangement?

| $a$ | $b$ | $c$ |
| :--- | :--- | :--- |
| $d$ | $e$ | $f$ |
| $g$ | $h$ | $i$ |

## Solution

See fig.

| $a$ | $h$ | $c$ |
| :--- | :--- | :--- |
| $f$ | $e$ | $d$ |
| $g$ | $b$ | $i$ |

## Answer

Yes.