3-5. Solve the system

\[
\left\{\begin{aligned}
x_{1}+2 x_{2}+2 x_{3}+\cdots+2 x_{100} & =1 \\
x_{1}+3 x_{2}+4 x_{3}+\cdots+4 x_{100} & =2 \\
x_{1}+3 x_{2}+5 x_{3}+\cdots+6 x_{100} & =3 \\
\cdots & \cdots \\
x_{1}+3 x_{2}+5 x_{3}+\cdots+199 x_{100} & =100
\end{aligned}\right.
\]
Solve 5. Answer: \(x_{1}=x_{3}=\cdots=x_{99}=-1, x_{2}=x_{4}=\cdots=x_{100}=1\). The solution is similar to the solution of problem 5 for 7th grade.

\section*{9th grade}