3 ms·

1+9=10

• ChainOfFools 3y ago
  i'm not sure what you are demonstrating? 1 sums digitwise to 1 1 + (10-1) = 10 which also sums to 1 in the same way
• semiquaver 3y ago
  1 = 1+0
• shermantanktop 3y ago
  Right, the digit sum of 10 is 1...perhaps I should have said "final digit sum." Same for 10000, or 1 with any number of zeroes after it. The point of this trickery is that N-1 added to any number is really adding N (which adds 1 to the second position, by definition) and adding -1 (which subtracts 1 from the first position). In base 10, this is the adding 9 trick. It can be extended by using any multiple of 9. That applies to the N-1 version, so that adding M*(N-1) to a base N number yields the same digit sum. 1+9 = 10 = 1 1 + 27 = 28 = 10 = 1 In hex: 1 + F = 10 = 1 1 + 2D = 2E = 10 = 1