The sum of the numbers A and B is a, and the number A is (2/5) of the number B, so what is the number A?
甲、乙两数的和是a，甲数是乙数的(2/5)，则甲数是多少．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<result>2/7 = around 0.285714</result>