A piece of steel is (4/5) meters long, if (1/2) meters are left after some of them are used up, how many meters are used up?
一根钢材长(4/5)米，若用去一些后还剩(1/2)米，用去了多少米．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

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

<gadget id="calculator">(4/5) - (1/2)</gadget>
<output>3/10 = around 0.3</output>

<result>3/10 = around 0.3</result>