A fraction is divided twice with 3, and divided once with 7 to get (2/5). What is the original fraction?
一个分数用3约分2次，用7约分1次后得到(2/5)，原来这个分数是多少？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>