1. Calculate: $3 \times 995 + 4 \times 996 + 5 \times 997 + 6 \times 998 + 7 \times 999 - 4985 \times 3=$
【Answer】 9980
【Analysis】Key point: Smart calculation
Method one: $3 \times 995+4 \times 996+5 \times 997+6 \times 998+7 \times 999-4985 \times 3$
$$
\begin{array}{l}
=(3+4+5+6+7) \times 997-3 \times 2-4 \times 1+6 \times 1+7 \times 2-5 \times 997 \times 3 \\
=25 \times 997-6-4+6+14-15 \times 997 \\
=(25-15) \times 997+10 \\
=9970+10 \\
=9980
\end{array}
$$

Method two: $3 \times(1000-5)+4 \times(1000-4)+5 \times(1000-3)+6 \times(1000-2)+7 \times(1000$
$$
\begin{aligned}
& -1)-(5000-15) \times 3 \\
= & 3000-15+4000-16+5000-15+6000-12+7000-7-15000+45 \\
= & 25000-15000-30-28-7+45 \\
= & 10000+15-35 \\
= & 10000-20 \\
= & 9980
\end{aligned}
$$