5,? 7,2,? eight

3,? 10,6,? nine

Tip: 1+2 =9+ 10? 3+4 = 1 1+ 12 ? 2+3 = 10 + 1 1

1+5 = 3+7 ? 2+6 = 4 + 8 5+9 = 7+ 1 1 ? 6+ 10 = 8+ 12

(The numbers in the equation represent the serial number positions marked in the figure below)