The sum of the numbers A and B is 500.5, and the decimal point of the number B is moved three places to the right to equal the number A. What is the number A?
甲、乙两数的和是500.5，乙数小数点向右移动三位就等于甲数，甲数是多少．
<gadget id="calculator">1 + 1_000</gadget>
<output>1_001</output>

<gadget id="calculator">500.5 / 1_001</gadget>
<output>0.5</output>

<gadget id="calculator">0.5 * 1_000</gadget>
<output>500</output>

<result>500</result>