After adding the same number to the numerator and denominator of (1/15), the fraction can be reduced to (4/11). What is the added number?
把(1/15)的分子、分母同时加上同一个数后，分数就可约简为(4/11)，所加的数是多少．
<gadget id="calculator">4 / 11</gadget>
<output>4/11 = around 0.363636</output>

<gadget id="calculator">(4/11) * 15</gadget>
<output>60/11 = around 5.454545</output>

<gadget id="calculator">(60/11) - 1</gadget>
<output>49/11 = around 4.454545</output>

<gadget id="calculator">1 - (4/11)</gadget>
<output>7/11 = around 0.636364</output>

<gadget id="calculator">(49/11) / (7/11)</gadget>
<output>7</output>

<result>7</result>