Express the decimal number `Dec` in binary notation (with no leading zeroes).

Find the largest power of 2 that will go into `Dec` and put a '1' in its place. (Binary place values: 32 16 8 4 2 1)

The largest power of 2 that goes into `Dec` is `Divisor` so put a 1 in the `Divisor`s place.

Subtract `Divisor` from `Dec` giving `Dec - Divisor`. Now find the largest power of 2 that goes into `Dec-Divisor` and put a 1 in its place.

Continue dividing and substracting until you get to the ones place (2 to the 0 power).

Add up all the powers of 2 that have a 1 in their place.

The answer is `Dec.toString(2)`