Question 119
$k$, $n$ are two arbitrary positive integers. Prove that there exists at least $(k-1)(n-k+1)$ positive integers that can be produced by $n$ number of $k$'s and using only $+$, $-$, $\times$, $\div$ operations and adding parentheses between them, but cannot be produced using $n-1$ number of $k$'s.