X-(4/5)X=(2/3).
X-(4/5)X=(2/3)．
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

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

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(2/3) / (1/5)</gadget>
<output>10/3 = around 3.333333</output>

<result>10/3 = around 3.333333</result>