Adding the same number to the numerator and denominator of the fraction (5/13) will result in (1/2). What is the number added at the same time?
分数(5/13)的分子和分母同时加上一个相同的数，约分后是(1/2)．同时加上的这个数是多少．
<gadget id="calculator">13 - 5</gadget>
<output>8</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">8 / 1</gadget>
<output>8</output>

<gadget id="calculator">8 - 5</gadget>
<output>3</output>

<result>3</result>