两位数加一位数(进位)、两位数减一位数(退位)共4套

90 - 9 = 9 + 68 = 77 - 8 = 91 + 9 =2 + 38 = 20 - 1 = 48 + 3 = 8 + 77 =40 - 3 = 39 + 2 = 62 - 4 = 68