A piece of rope is 180 meters long, 30% of the total length is used for the first time, and 40% of the total length is used for the second time, how many meters are left unused?
一段绳子长180米，第一次用去全长的30%，第二次用去全长的40%，还剩下多少米没用完？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">180 * (3/10)</gadget>
<output>54</output>

<result>54</result>