The engineering team wants to dig a (7/8) kilometer canal. They dug (1/4) kilometer on the first day and (2/5) kilometer on the second day. If it is required to finish digging on the third day, then How many kilometers should be dug on the third day?
工程队要挖一条(7/8)千米的水渠，第一天挖了(1/4)千米，第二天挖了(2/5)千米，如果要求第三天挖完，那么第三天应挖多少千米？
<gadget id="calculator">7 / 8</gadget>
<output>7/8 = around 0.875</output>

<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">(7/8) - (1/4) - (2/5)</gadget>
<output>9/40 = around 0.225</output>

<result>9/40 = around 0.225</result>