A village is building a canal (4/5) kilometers long. On the first day (1/4) of the full length was built, and on the second day (3/10) of the full length was built. What fraction is left unrepaired?
某村修一条长(4/5)千米的水渠，第一天修了全长的(1/4)，第二天修了全长的(3/10)，还剩几分之几没有修？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">1 - (1/4) - (3/10)</gadget>
<output>9/20 = around 0.45</output>

<result>9/20 = around 0.45</result>