7. If the price of an item after a 50% discount differs from the price after a 30% discount by **81** yuan, then the price of the item after an 80% discount is ( ) yuan. Exam point: Economic problems
【Analysis】Solution: Let the price be $\mathrm{x}$ yuan, then
$$
\begin{aligned}
0.7 x-0.5 x & =81 \\
0.2 x & =81 \\
x & =405
\end{aligned}
$$

20% discount: $405 \times 0.8=324$ yuan