The size we wear usually uses "yard" or "centimeter" as the unit, and the conversion relationship between them is b=2a-10 (b represents the number of sizes, a represents the number of centimeters). Then how many yards are the 25cm shoes using "yard" as the unit.
我们所穿的尺码通常用"码"或"厘米"作单位，它们之间的换算关系是b=2a-10(b表示尺码数，a表示厘米数)．那么25厘米的鞋子用"码"作单位就是多少码．
<gadget id="calculator">2 * 25</gadget>
<output>50</output>

<gadget id="calculator">50 - 10</gadget>
<output>40</output>

<result>40</result>