If the denominator of fraction (2/5) is increased by 5, how much should the numerator be increased to keep the fraction value unchanged.
分数(2/5)分母增加5，分子应该增加多少，才能使分数值不变．
<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<result>2</result>