Add the same natural number to the numerator and denominator of (1/7) to get the fraction (3/5). What is the natural number?
将(1/7)的分子分母同时加上一个相同的自然数后得到分数(3/5)，这个自然数是多少．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">7 / 1</gadget>
<output>7</output>

<gadget id="calculator">(3/5) * 7</gadget>
<output>21/5 = around 4.2</output>

<gadget id="calculator">(21/5) - 1</gadget>
<output>16/5 = around 3.2</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(16/5) / (2/5)</gadget>
<output>8</output>

<result>8</result>