Step 1:
The first step to converting 665.3984125 to a fraction is to re-write 665.3984125 in the form p/q where p and q are both positive integers. To start with, 665.3984125 can be written as simply 665.3984125/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 665.3984125, which in this case is 7. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 665.3984125/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 665.3984125/1 each by 10000000:
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 665.3984125 as a fraction:
81844/123 / 1