((1/11)+(1/21)+(1/31)+(1/41))*((1/21)+(1/31)+(1/41)+(1/51) )-((1/11)+(1/21)+(1/31)+(1/41)+(1/51))*((1/21)+(1/31)+(1/ 41)).
((1/11)+(1/21)+(1/31)+(1/41))*((1/21)+(1/31)+(1/41)+(1/51))-((1/11)+(1/21)+(1/31)+(1/41)+(1/51))*((1/21)+(1/31)+(1/41))．
<gadget id="calculator">1 / 11</gadget>
<output>1/11 = around 0.090909</output>

<gadget id="calculator">1 / 21</gadget>
<output>1/21 = around 0.047619</output>

<gadget id="calculator">1 / 31</gadget>
<output>1/31 = around 0.032258</output>

<gadget id="calculator">1 / 41</gadget>
<output>1/41 = around 0.02439</output>

<gadget id="calculator">(1/11) + (1/21) + (1/31) + (1/41)</gadget>
<output>57_304/293_601 = around 0.195176</output>

<gadget id="calculator">1 / 51</gadget>
<output>1/51 = around 0.019608</output>

<gadget id="calculator">(1/21) + (1/31) + (1/41) + (1/51)</gadget>
<output>18_736/151_249 = around 0.123875</output>

<gadget id="calculator">(57_304/293_601) * (18_736/151_249)</gadget>
<output>1_073_647_744/44_406_857_649 = around 0.024178</output>

<gadget id="calculator">(1/11) + (1/21) + (1/31) + (1/41) + (1/51)</gadget>
<output>357_345/1_663_739 = around 0.214784</output>

<gadget id="calculator">(1/21) + (1/31) + (1/41)</gadget>
<output>2_783/26_691 = around 0.104267</output>

<gadget id="calculator">(357_345/1_663_739) * (2_783/26_691)</gadget>
<output>30_136_095/1_345_662_353 = around 0.022395</output>

<gadget id="calculator">(1_073_647_744/44_406_857_649) - (30_136_095/1_345_662_353)</gadget>
<output>1/561 = around 0.001783</output>

<result>1/561 = around 0.001783</result>