A piece of iron wire is 50 meters long. If (2/5) is used for the first time, how many meters will be used again to leave exactly half of the iron wire?
一根铁丝长50米，第一次用去(2/5)，再用去多少米正好剩下这根铁丝的一半？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">50 * (1/10)</gadget>
<output>5</output>

<result>5</result>