The word digit means a single figure number: The numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 are all digits. Big numbers can be reduced to single digit by adding the constituents.
Digit Sum:A digit sum is the sum of all the digits of a number and is found by adding all of the digits of a number
● Keep finding the digit sum of the result + until it’s less than 10
● 0 and 9 are equivalent
Look and understand some more example :
To find the digit sum of 18, for the example we just add 1 and 8, i.e.1 + 8 =9 so the digit sum of 18 is 9. And the digit sum of 234 is 9 because 2 + 3+ 4 = 9
Practise it: hold numbers in your head while you add them in the arithmetic memory game.