Kovaldzhi A.k.

A hundred people answered the question: "Will the new president be better than the previous one?" Of them, $a$ people think it will be better, $b$ - that it will be the same, and $c$ - that it will be worse. Sociologists constructed two "optimism" indicators of the respondents: $m=a+b / 2$ and $n=a-c$. It turned out that $m=40$. Find $n$.
We know that $a+b+c=100$ and $2a+b=80$. By subtracting the first equation from the second, we have: $a-c=-20$.

## Otвет

$n=-20$.