Using the ciphers 1 up to 9, three numbers (of three ciphers each) can be formed, such that the second number is twice the first number, and the third number is three times the first number. Which are these three numbers?

One Answer on this Question

1. The 3-digit number can be written as the sequence [n, 2n, 3n]
   n = 1 → [1, 2, 3] → valid
   n = 2 → [2, 4, 6] → valid
   n = 3 → [3, 6, 9] → valid

   n = 4 → [4, 8, 12] is not valid because this would lead to a 4-digit number
   any value of n > 4 would also produce invalid answer

   Answer: Three numbers: {123, 246, 369}

   Reply