There is a box of biscuits, Xiao Ming can eat it for 25 days by himself, if he eats it with his mother, he can eat it for 20 days, if his mother eats this box of biscuits alone, how many days can he eat it.
有一盒饼干，小明一个人吃可以吃25天，如果和妈妈一起吃，那么可以吃20天，如果妈妈一个人吃这盒饼干，可以吃多少天．
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 25</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">(1/20) - (1/25)</gadget>
<output>1/100 = around 0.01</output>

<gadget id="calculator">1 / (1/100)</gadget>
<output>100</output>

<result>100</result>