Sum of Digits of a Number is called Digit Sum.
¶ Addition and Subtraction (0)=(9)
¶ Digit Sum can be Negative .
E.g.-: 4372-4328=44
Digit Sum 7-8=8
Digit Sum -1=8
-1+9=8 {L.H.S=R.H.S]
(Always Add 9 to the negative Digit Sum)
¶ L.H.S = R.H.S(
Addition(+),Substraction(-) and multiplication(✖️)
Example-1:
13+12=25 =>
Digit Sum 4 + 3 = 7(L.H.S = R.H.S)
¶ You can use Digit Sum in Percentage(%) & Decimal (.)
.

¶ Division

-: If denominator of a fraction digit sum is 2,4,7,8 than we have to multiply both nominator & denominator respectively (2✖️5),(4✖️7),(7✖️4),(8✖️8)

Example: 1/2 => 1✖️5/2✖️5
=5/1=>Digit Sum=5
2+4/7=> Digit Sum= 2 + 4✖️4/7✖️4= 7/1=>2+7=9 or 0