The age difference between mother and daughter is 20 years, and the age ratio of mother and daughter is 3:1, so how old is the daughter?
母女俩的年龄差是20岁，母女年龄的比是3：1，那么女儿多少岁．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">20 / (2/3)</gadget>
<output>30</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<result>10</result>