It is known that ((a)/10), ((b)/12), ((c)/21) are the three simplest true fractions, their product is (1/2), the difference between the largest number and the smallest number how many.
已知((a)/10)，((b)/12)，((c)/21)是三个最简真分数，他们的乘积是(1/2)，最大数与最小数的差是多少．
<gadget id="calculator">7 / 18</gadget>
<output>7/18 = around 0.388889</output>

<result>7/18 = around 0.388889</result>