bundle of wires is (1/2) meter long, 20% of the total length is used for the first time, and (1/4) meter is used for the second time, how many meters are left?
一捆电线长(1/2)米，第一次用去全长的20%，第二次用去(1/4)米，还剩下多少米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

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

<gadget id="calculator">(1/2) - (1/10) - (1/4)</gadget>
<output>3/20 = around 0.15</output>

<result>3/20 = around 0.15</result>