Xiao Ming buys a book and reads (2/5) of the whole book on the first day. He only needs to read 25 pages to read half of it. How many pages has he read?
小明买回一本书，第一天就读了全书的(2/5)，只要再读25页就读一半，他己读了多少页？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">25 / (1/10)</gadget>
<output>250</output>

<gadget id="calculator">250 * (2/5)</gadget>
<output>100</output>

<result>100</result>