What is 12345679 times 9?

Answer 1

111 111 111

If you multiply 12345679 by any two digit number* where the first digit is less than 9 and the sum of the digits is 9 (eg 36), the answer will consist of a single digit repeated 9 times. This will be the first digit of the two digit number plus 1 (eg multiplying by 36 will create an number consisting of only the digit 3+1 = 4: 12345679 x 36 = 444 444 444).

*Multiplying by 9 is multiplying by the "two" digit number "09", giving an answer consisting of the single digit 0+1 = 1 repeated.