We can read off the fraction field from the standard representation:

                (-1)0 * 1.100101 * 25

The fraction field is just the part to the right of the decimal point
but extended for 23 bits

             frac: 100101...

where the ... is just 17 more 0's to make a total of 23 bits for f

The final bit representation of 100.5 is then

        s     exp         frac
        0  1000 0100    100101...
                               17 more 0's

or 

        010000100100101...
                       17 more 0's