A's number is 415, which is 20% less than B's number. What is B's number?
甲数是415，比乙数少20%，乙数是多少．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">415 / (4/5)</gadget>
<output>2_075/4 = around 518.75</output>

<result>2_075/4 = around 518.75</result>