Xiaogang reads an extra-curricular book. He reads the whole book (2/5) on the first day and (3/7) the whole book on the second day. How much of this book did Xiaojun read in two days?
小刚看一本课外书，第一天看了全书的(2/5)，第二天看了全书的(3/7)．小军两天一共看了这本书的几分之几？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">(2/5) + (3/7)</gadget>
<output>29/35 = around 0.828571</output>

<result>29/35 = around 0.828571</result>