piece of iron sheet, (3/8) of it is used for the first time, and (1/5) of it is used for the second time, how much of the iron sheet is left.
一张铁皮，第一次用去它的(3/8)，第二次用去它的(1/5)，还剩这张铁皮的多少．
<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (3/8) - (1/5)</gadget>
<output>17/40 = around 0.425</output>

<result>17/40 = around 0.425</result>