Construct a grammar for $\{a^n(bc)^m : m,n \ge 1, m < n/2\}$
Let $n = n'+1$, $m = m'+1$. Then $m &lt; n/2$ translates to $n'+ 1 &gt; 2(m+1)$, i.e. $n' \geq 2m'+2$. Therefore we can write the language as
$$
\{ a^{1+2m'+2+k}(bc)^{1+m'} : m',k \geq 0 \} =
\{ a^3 a^k (a^2)^{m'} (bc)^{m'} bc : m',k \geq 0 \}.
$$
You take it from here.