Step 1:
The first step to converting 128639.68404685 to a fraction is to re-write 128639.68404685 in the form p/q where p and q are both positive integers. To start with, 128639.68404685 can be written as simply 128639.68404685/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 128639.68404685, which in this case is 8. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 128639.68404685/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 128639.68404685/1 each by 100000000:
Step 3:
Now the last step is to simplify the fraction (if possible) by finding similar factors and cancelling them out, which leads to the following answer for 128639.68404685 as a fraction:
385919/3 / 1