The number A (1/2) is equal to 20% of the number B. The number B is 100. What is the number A?
甲数(1/2)的与乙数的20%相等，乙数是100，甲数是多少．
<gadget id="calculator">20 / 100</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>2/5 = around 0.4</output>

<gadget id="calculator">100 * (2/5)</gadget>
<output>40</output>

<result>40</result>