THE NUMERAL 425D63 IS DIVISIBLE BY 3. WHAT IS 
THE SUM OF THE POSSIBLE DIGITS FOR D?

For an integer to be divisible by 3, the
sum of its digits must be divisible by 3

(Sum of digits of 425D63) = 4 + 2 + 5 + D + 6 + 3 = 20 + D

Since 0 < D < 9

Build the D in the middle up to 20 + D, the sum of the digits,
by adding 20 to all three sides

     20 < 20 + D < 29

The only integers between 20 and 29, inclusive,
that are divisible by 3 are 21, 24, and 27. So

Sum of digits = 20 + D = 21, 24, or 27

If 20 + D = 21 then D = 1
If 20 + D = 24 then D = 4
If 20 + D = 27 then D = 7

Possible digits for D are 1, 4, and 7
Their sum is 1 + 4 + 7 = 12

Edwin