The number A is equal to 20% of the number B, the number B is 400, what is the number A?
甲数与乙数的20%相等，乙数是400，甲数是多少．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">400 * (1/5)</gadget>
<output>80</output>

<result>80</result>