After adding the same number to the numerator and denominator of (5/23), it can be divided into (2/5). What is the added number?
把(5/23)的分子和分母同时加上同一个数后，正好可以约分成(2/5)，加上的这个数是多少？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) * 23</gadget>
<output>46/5 = around 9.2</output>

<gadget id="calculator">(46/5) - 5</gadget>
<output>21/5 = around 4.2</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

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

<result>7</result>