$$
\begin{aligned}
& 1891-\left(1600: 40+8040^{5}: 40\right)^{4} \times 4= \\
& =1891-(40+201) \times 4= \\
& =1891-241 \times 4=1891-964=927 .
\end{aligned}
$$

Based on the properties of arithmetic operations, we can write:

$$
\begin{aligned}
& 1891-(1600: a+8040: a) \times c= \\
& =1891-(8040: a+1600: a) \times c= \\
& =1891-((1600+8040): a) \times c= \\
& =1891-(1600: a) \times c-(8040: a) \times c= \\
& =1891-(1600 \times c): a-(8040 \times c): a= \\
& =1891-(1600 \times c+8040 \times c): a
\end{aligned}
$$

Answer: 927.
2. Arrange the order of operations in the expression

$$
1891-(1600: a+8040: a) \times c .
$$

and calculate its value when $a=40$ and $c=4$. Show how the expression can be modified without changing its numerical value.