Question 577028
A+A=A for the ones digit means {{{highlight(A=0)}}}
O cannot be 0 too, so for the hundreds digit O+O+1(carried over)=10+O, so {{{highlight(O=9)}}}
(2O+1=10+O --> O+1=10 --> O=9)
At the same time, as 9+9+1(carried over)=19 when adding the hundreds, there is 1 carried over to the thousands
Because there was that 1 carried over from the sum of the tens digit, C+L=10+D.
And since {{{D>=1}}}, {{{C+L>=11}}}
For the thousands digit C+C+1 (carried over)=S<9 --> 2C+1=S<9 so C<4
If C<4 and {{{C+L>=11}}}, then L>7.
Since L cannot be 9, because O=9, then {{{highlight(L=8)}}}
And since {{{C+L>=11}}}, then {{{highlight(C=3)}}},
and C+L=11=10+D so {{{highlight(D=1)}}}
and 2C+1=S gives us S=2(3)+1=6+1, so {{{highlight(S=7)}}}.
{{{addition(3930,3980)}}}