A book is priced at 15 yuan, and you can make a profit of 50% if you sell it. If you sell it at a 20% discount, how much can you earn for a book?
一本书定价15元，售出可获利50%，如果打八折卖，一本可赚多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">15 * (4/5)</gadget>
<output>12</output>

<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 + (1/2)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">15 / (3/2)</gadget>
<output>10</output>

<gadget id="calculator">12 - 10</gadget>
<output>2</output>

<result>2</result>