(19/20) minus (13/20), and how much to subtract, the difference is (1/5).
(19/20)减去(13/20)，再减去多少，差是(1/5)．
<gadget id="calculator">19 / 20</gadget>
<output>19/20 = around 0.95</output>

<gadget id="calculator">13 / 20</gadget>
<output>13/20 = around 0.65</output>

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

<gadget id="calculator">(19/20) - (13/20) - (1/5)</gadget>
<output>1/10 = around 0.1</output>

<result>1/10 = around 0.1</result>