20% of a number is 40, what is 50% of this number?
一个数的20%是40，这个数的50%是多少．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">40 / (1/5)</gadget>
<output>200</output>

<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">200 * (1/2)</gadget>
<output>100</output>

<result>100</result>