The original price of a book is 20 yuan, and the current price is 15 yuan. How much has the price been reduced?
一本书原价是20元，现价15元，降价了多少．
<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<gadget id="calculator">5 / 20</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>