The number A is 40, which is exactly 50% of the number B. What is the number B?
甲数是40，正好是乙数的50%，乙数是多少．
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">40 / (1/2)</gadget>
<output>80</output>

<result>80</result>