Step 1:
The first step to converting 648.21100810585 to a fraction is to re-write 648.21100810585 in the form p/q where p and q are both positive integers. To start with, 648.21100810585 can be written as simply 648.21100810585/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 648.21100810585, which in this case is 11. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 648.21100810585/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 648.21100810585/1 each by 100000000000:
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 648.21100810585 as a fraction:
12316/19 / 1