book, Xiaomao read (1/3) on the first day and the whole book (2/5) on the second day, how much of the whole book is left
一本书，小毛第一天看了(1/3)，第二天看了全书的(2/5)，还剩全书的多少
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/3) - (2/5)</gadget>
<output>4/15 = around 0.266667</output>

<result>4/15 = around 0.266667</result>