The age of the son this year is (1/4) of the age of the father. After 10 years, the age of the son will be (2/5) of the age of the father. How old is the son this year?
今年儿子的年龄是父亲年龄的(1/4)，10年后，儿子的年龄是父亲年龄的(2/5)，今年儿子多少岁？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">10 * (2/5)</gadget>
<output>4</output>

<gadget id="calculator">10 - 4</gadget>
<output>6</output>

<gadget id="calculator">4 * (2/5)</gadget>
<output>8/5 = around 1.6</output>

<gadget id="calculator">(8/5) - 1</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">6 / (3/5)</gadget>
<output>10</output>

<result>10</result>