story book, Xuanxuan read the whole book (2/7) on the first day, the rest (1/3) on the second day, and some of the whole book on the second day.
一本故事书，宣宣第一天看了全书的(2/7)，第二天看了剩下的(1/3)，第二天看了全书的多少．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (2/7)</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 * (5/7) * (1/3)</gadget>
<output>5/21 = around 0.238095</output>

<result>5/21 = around 0.238095</result>