The thickness of each book is about 25 mm. How many centimeters are the total thickness of 4 such books?
一种书每本的厚度约是25毫米，4本这样的书一共厚多少厘米
<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">25 * (2/5)</gadget>
<output>10</output>

<result>10</result>