Step 1:
The first step to converting 840.421 to a fraction is to re-write 840.421 in the form p/q where p and q are both positive integers. To start with, 840.421 can be written as simply 840.421/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 840.421, which in this case is 3. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 840.421/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 840.421/1 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 840.421 as a fraction:
15968/19 / 1