Step 1:
The first step to converting 621.78156406129 to a fraction is to re-write 621.78156406129 in the form p/q where p and q are both positive integers. To start with, 621.78156406129 can be written as simply 621.78156406129/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 621.78156406129, which in this case is 11. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 621.78156406129/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 621.78156406129/1 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 621.78156406129 as a fraction:
19897/32 / 1