If a number is reduced by 10 times and expanded by 1000 times, it becomes 4,000. What is the original number?
一个数缩小10倍，又扩大1000倍后是0.4万，原来的数是多少．
<gadget id="calculator">0.4 * 10_000</gadget>
<output>4_000</output>

<gadget id="calculator">4_000 / 1_000</gadget>
<output>4</output>

<gadget id="calculator">4 * 10</gadget>
<output>40</output>

<result>40</result>