If a book of 50 yuan is sold at a discount of 25%, what is the selling price?
50元的一本书打七五折出售，则售价是多少元．
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">50 * (3/4)</gadget>
<output>75/2 = around 37.5</output>

<result>75/2 = around 37.5</result>