Subtract the sum of (1/4) and (1/5) from a number, the difference is (1/2), what is this number?
从一个数里减去(1/4)与(1/5)的和，差是(1/2)，这个数是多少？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<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">(1/2) + (9/20)</gadget>
<output>19/20 = around 0.95</output>

<result>19/20 = around 0.95</result>