(4+(1/5)+(1/6)+(1/7))*((1/5)+(1/6)+(1/7)+(1/8))-(4 +(1/5)+(1/6)+(1/7)+(1/8))*((1/5)+(1/6)+(1/7)).
(4+(1/5)+(1/6)+(1/7))*((1/5)+(1/6)+(1/7)+(1/8))-(4+(1/5)+(1/6)+(1/7)+(1/8))*((1/5)+(1/6)+(1/7))．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">4 + (1/5) + (1/6) + (1/7)</gadget>
<output>947/210 = around 4.509524</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/5) + (1/6) + (1/7) + (1/8)</gadget>
<output>533/840 = around 0.634524</output>

<gadget id="calculator">(947/210) * (533/840)</gadget>
<output>504_751/176_400 = around 2.8614</output>

<gadget id="calculator">4 + (1/5) + (1/6) + (1/7) + (1/8)</gadget>
<output>3_893/840 = around 4.634524</output>

<gadget id="calculator">(1/5) + (1/6) + (1/7)</gadget>
<output>107/210 = around 0.509524</output>

<gadget id="calculator">(3_893/840) * (107/210)</gadget>
<output>416_551/176_400 = around 2.3614</output>

<gadget id="calculator">(504_751/176_400) - (416_551/176_400)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>