There is a two-digit number, add a decimal point in front of its one-digit number, and add it to this number, the result is 20.9, what is the two-digit number?
有一个两位数，在它的个位数字的前面加上一个小数点，再和这个数相加，得数是20.9，这个两位数是多少？
<gadget id="calculator">1 + 0.1</gadget>
<output>1.1</output>

<gadget id="calculator">20.9 / 1.1</gadget>
<output>19</output>

<result>19</result>