5). 0 + 2 + 4 + 6 + 8 - 5 × 4 = 20 - 20 = 0
6). prima zi = 2 probleme
2 × 2 = 4 probleme ( a 2 a zi )
4 × 2 = 8 probleme ( a 3 a zi )
8 × 2 = 16 probleme ( a 4 a zi )
2 + 4 + 8 + 16 = 30 probleme ( in total rezolvate )
7). 5 × 3 = 15 poze ( cu animale )
5 + 15 = 20 poze ( necesare )