29.1. Find the three-digit number $\overline{a b c}$, if it is known that

$$
\begin{gathered}
8 a+5 b+c=100 \\
a+b+c=20
\end{gathered}
$$
29.1. Subtracting the second equation of the system from the first, we get

$$
7 a+4 b=80
$$

From this equality, it follows that $a$ is divisible by 4, i.e., $a=4$ or $a=8$. But $a$ cannot be equal to 4, because in this case, from the equation $7 a+4 b=80$, it would follow that $b=13$. However, this is impossible, since $b$ is a digit, i.e., $b \leqslant 9$. Therefore, $a=8$. Then from the equation $7 a+4 b=80$, it follows that $b=6$. Finally, from the equation $a+b+c=20$, we find that $c=6$. Answer: 866.