Workers repair a road with a total length of a kilometer, and repair the full length (1/4) in the first week, repair the full length (1/3) in the second week, and repair the full length (1/5) in the third week. How many kilometers are left unrepaired.
工人修全长为a千米的公路，第一周修了全长的(1/4)，第二周修了全长的(1/3)，第三周修了全长的(1/5)．还剩下多少千米没有修．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

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

<gadget id="calculator">1 - (1/4) - (1/3) - (1/5)</gadget>
<output>13/60 = around 0.216667</output>

<result>13/60 = around 0.216667</result>