Ans: (a) $\$300$ (b) $\$400$
- The selling price of the book
$\begin{array}{cl}
= & 250 \times (1+20\%) \\
= & \$ 300
\end{array}$ - The marked price of the book
$\begin{array}{cl}
= & 300 \div (1 – 25\%) \\
= & \$ 400
\end{array}$
