Step 1:
The first step to converting 15940.421 to a fraction is to re-write 15940.421 in the form p/q where p and q are both positive integers. To start with, 15940.421 can be written as simply 15940.421/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 15940.421, which in this case is 3. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 15940.421/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 15940.421/1 each by 1000:
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 15940.421 as a fraction:
111583/7 / 1