A bag of salt weighs (6/7) kilograms, if (1/7) is used up, how much of the total amount is left
一袋盐重(6/7)千克，如果用去(1/7)，还剩总数的多少
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 - (1/7)</gadget>
<output>6/7 = around 0.857143</output>

<result>6/7 = around 0.857143</result>