A vegetable field has (8/9) hectares, cabbage occupies (1/4), radish occupies (2/5), how much is left?
一块菜地有(8/9)公顷，白菜占(1/4)，萝卜占(2/5)，还剩下几分之几？
<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>

<result>7/20 = around 0.35</result>