The digital root of a number is obtained by summing its digits and then repeating the process (summing the sum's digits) until the answer is a single digit number. For example, the digital root of 7368 is 6.

Determine the digital root of (9⁷²⁴⁰+38)⁸⁴⁵⁷

if S(x)=digital root of x

 then there are two properties you can use
s(a+b)=s(s(a)+s(b))
s(ab)=s(s(a)s(b))

:-D

Posted by Daniel on 2006-06-29 11:43:35