The son's age this year is the father's (1/4), and 10 years later, the son's age is the father's (2/5), how old is the son this year?
今年儿子的年龄是父亲的(1/4)，10年后，儿子的年龄是父亲的(2/5)，今年儿子几岁？
<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>