The decimal point of a certain number is moved one place to the right, which is 18.9 larger than the original number. What is the original number?
某数的小数点向右移一位，比原数大18.9，原数是多少．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">18.9 / 9</gadget>
<output>2.1</output>

<result>2.1</result>