After a three digit number is multiplied by 13, the last three digits of the product are 123. Find this number
Let the value of the first few digits of the product be X. then there are: 100 ≤ (1000x + 123) △ 13 ≤ 999. Obviously, 2 ≤ x ≤ 12 is transformed into: 100 ≤ 77X + 9 - (x - 6) / 13 ≤ 999. If (x - 6) / 13 is an integer, x = 6, 19, 32 The number combination of equal shape such as 13T + 6 is 2 ≤ x ≤ 12