A book is priced at 50 yuan. If you sell it at this price, you can make a profit of 25%. If you sell it at this price with a 10% discount, how much profit can you make?
一本书定价50元，如果按这个定价售出，可获利25%，如果按这个定价打九折售出，还可获利多少元？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">50 / (5/4)</gadget>
<output>40</output>

<gadget id="calculator">45 - 40</gadget>
<output>5</output>

<result>5</result>