Ans: (a) $\$320$ (b) $28\%$
- The selling price of the vase
$\begin{array}{cl}
= & \$400 \times (1-20\%) \\
= & \$320
\end{array}$ - The cost of the vase
$\begin{array}{cl}
= & \$320 – \$70 \\
= & \$250
\end{array}$Therefore the percentage profit
$\begin{array}{cl}
= & \dfrac{70}{250} \times 100\% \\
= & 28\%
\end{array}$