1 0 “ ” 2 2011 12 8 2011 9 30 3 4 5 6 1972 12 7 2009 1 15 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 × ÷ 1 42 ÷ 2 2 = 43 0