((17/20)-((2/5)+(1/4)))/(4/5).
((17/20)-((2/5)+(1/4)))/(4/5)．
<gadget id="calculator">17 / 20</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(2/5) + (1/4)</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">(17/20) - (13/20)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(1/5) / (4/5)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>