Observe and think to find the law, fill in the appropriate number (4/5), (2/5), (1/5), how much, (1/20).
观察思考找规律，填上合适的数(4/5)，(2/5)，(1/5)，多少，(1/20)．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/5) * (1/2)</gadget>
<output>1/10 = around 0.1</output>

<result>1/10 = around 0.1</result>