The number A is 80% of the number B. If the number A is 40, what is the number B?
甲数是乙数的80%，若甲数是40，那么乙数是多少
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">40 / (4/5)</gadget>
<output>50</output>

<result>50</result>