A road repair team repairs a 20-kilometer road. On the first day, it repairs the full length (1/4), and on the second day it repairs the full length (2/5). How many kilometers are left to be repaired?
一个修路队修一条长20千米的公路，第一天修了全长的(1/4)，第二天修了全长的(2/5)，还剩下多少千米没有修完？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) + (2/5)</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">1 - (13/20)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">20 * (7/20)</gadget>
<output>7</output>

<result>7</result>