2. The magpie-crow was cooking porridge, feeding her chicks. The third chick received as much porridge as the first two combined. The fourth chick received as much as the second and third. The fifth chick received as much as the third and fourth. The sixth chick received as much as the fourth and fifth. The seventh chick got nothing - the porridge ran out! It is known that the fifth chick received 10 grams of porridge. How much porridge did the magpie-crow cook?
Answer: 40 g.

Solution. Let the first chick receive a grams of porridge, the second - b grams, Then the others received $\mathrm{a}+\mathrm{b}, \mathrm{a}+2 \mathrm{~b}, 2 \mathrm{a}+3 \mathrm{~b}, 3 \mathrm{a}+5 \mathrm{~b}, 0$ grams respectively. In total, they received $8 \mathrm{a}+12 \mathrm{~b}$ grams of porridge, which is 4 times more than what the fifth one received.