When Xiao Ming calculated the addition of two numbers, he mistakenly took the 1 in the percentile of one addend as 7, and the 8 in the tenth place of the other addend as 3, and the sum obtained was 19.96. What is the sum of the original two-digit sum?
小明在计算两个数相加时，把一个加数百分位上1错误地当7，把另一个加数十分位上的8错误地当作3，所得的和是19.96．原来两位数相加的和应是多少．
<gadget id="calculator">0.8 - 0.3</gadget>
<output>0.5</output>

<gadget id="calculator">0.07 - 0.01</gadget>
<output>0.06</output>

<gadget id="calculator">0.5 - 0.06</gadget>
<output>0.44</output>

<gadget id="calculator">19.96 + 0.44</gadget>
<output>20.4</output>

<result>20.4</result>