23. $\mathbf{E}$
Since $c$ is the digit in the hundreds column of the answer, we can deduce that $c>a$. Therefore, there must be a carry from the units column to the tens column and hence $a=4-1=3$. Since there will also be a carry from the tens column to the hundreds column, we have $c=a+a+1=7$. Therefore, $7+b=13$ and hence $b=6$. Therefore the value of $a+b+c$ is $3+6+7=16$.
23. In the addition sum below, $a, b$ and $c$ stand for different digits.
What is the value of $a+b+c$ ?
A 20
B 19
C 18
D 17
E 16