If a number is multiplied by the sum of (2/3) and (4/7), the product obtained is 1. What is the number?
一个数乘(2/3)与(4/7)的和，所得的积是1，这个数是多少．
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(2/3) + (4/7)</gadget>
<output>26/21 = around 1.238095</output>

<gadget id="calculator">1 / (26/21)</gadget>
<output>21/26 = around 0.807692</output>

<result>21/26 = around 0.807692</result>