Digging a 20-kilometer canal, the full length (1/4) was dug on the first day, and the full length (1/5) was dug on the second day. How many kilometers were dug in total in two days?
挖一条20千米的水渠，第一天挖了全长的(1/4)，第二天挖了全长的(1/5)．两天一共挖了多少千米？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) + (1/5)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">20 * (9/20)</gadget>
<output>9</output>

<result>9</result>