Assume that A B C and D are all single digit whole numbers I

Assume that A, B, C, and D are all single digit whole numbers. If, which single digit number is represented by each of the letters A, B, C, and D? A = B = C = D =

Solution

D+D =A and DD +DD =...DA

As A , D are single digits , D is greater than 5 .

Trying D =5,6,7,8,9, with DD +DD=...DA,

(for example D=7 does not fit as 77+77 =154 and 7 not equal to 5).

We are forced to conclude D =9 (99+99=198).

Hence ADD is 899 and as 899+899 =   1798,

the solution is

A =8,

B= 7 ,

C =1

and D =9