The price of a book is 30 yuan, and you can make a profit of 50% after selling it. If you sell it at 30% off the price, how much profit can you make?
一本书的定价是30元，售出后可获利50%，如果按定价的七折出售，可获利多少元？
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">30 * (7/10)</gadget>
<output>21</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">30 / (3/2)</gadget>
<output>20</output>

<gadget id="calculator">21 - 20</gadget>
<output>1</output>

<result>1</result>