The engineering team wants to lay a gas pipeline. It was laid on the first day (1/10), on the second day (1/5), and on the third day (3/10). How much is left to be laid?
工程队要铺一条煤气管道，第一天铺了(1/10)，第二天铺了(1/5)，第三天铺了(3/10)，还有多少未铺？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (1/10) - (1/5) - (3/10)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>