A fraction is simplified to (3/7). It is known that the sum of the numerator and denominator is 120. What is the fraction?
一个分数化简后为(3/7)，已知分子与分母的和为120，这个分数为多少．
<gadget id="calculator">7 + 3</gadget>
<output>10</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">120 * (7/10)</gadget>
<output>84</output>

<gadget id="calculator">(3/10) / 84</gadget>
<output>1/280 = around 0.003571</output>

<gadget id="calculator">120 * (1/280)</gadget>
<output>3/7 = around 0.428571</output>

<result>3/7 = around 0.428571</result>