Iam learning floating point representation.I have two doubts, plz help,

1)0 10010011 10100010000000000000000 = 1.1010001 * 2 exp 20 = 1.638125 * 2 exp 23

Here 1010001 is mantissa part and 20 is exponent part , so 1.1010001 * 2 exp 20 but how this is equal to 1.638125 * 2 exp 23 . And also we need in decimal but 1.638125 * 2 exp 23 instead 1.638125 * 10 exp 23 .
How i interpreted is
1.1010001 * 2 exp 20 = 11010001 * 2 exp 13 = 209 * 2 exp 13 or 209 * 10 exp 13?

iam very confused...


2) 1.11....1(23 1's) = (2-2 exp(-23))