There is an iron wire, the first use of the full length (1/5), the second use of the full length (2/5), the third use of (3/10) meters, just used up, this one How many meters is the wire long?
有一根铁丝，第一次用去全长的(1/5)，第二次用去全长的(2/5)，第三次用去(3/10)米，正好用完，这根铁丝长多少米？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

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

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/5) - (2/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/10) / (2/5)</gadget>
<output>3/4 = around 0.75</output>

<result>3/4 = around 0.75</result>