Step 1:
The first step to converting 78921.789819405 to a fraction is to re-write 78921.789819405 in the form p/q where p and q are both positive integers. To start with, 78921.789819405 can be written as simply 78921.789819405/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 78921.789819405, which in this case is 9. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 78921.789819405/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 78921.789819405/1 each by 1000000000:
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 78921.789819405 as a fraction:
315687/4 / 1