3 ms·

An alternative way (but more intuitive) to find approx a / 9 in your head: result = (a x 0.1) + (a x 0.01) + ... so e.g. take a random number, 22103 answer is

• lotharbot 15y ago
  To be more complete: .1a + .01a + ... + (digit sum / 9) will give it to you. That's actually what this method is doing, it's just poorly explained. 22103/9 = 2210 + 221 + 22 + 2 + (2+2+1+0+3)/9 = 2455 + 8/9 So your ones digit ends up being 2+2+1+0+(any whole part left over from the digit sum), your tens digit is 2+2+1, your hundreds digit is 2+2, and your thousands digit is just 2.