Step 1:
The first step to converting 688.21423497909 to a fraction is to re-write 688.21423497909 in the form p/q where p and q are both positive integers. To start with, 688.21423497909 can be written as simply 688.21423497909/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 688.21423497909, which in this case is 11. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 688.21423497909/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 688.21423497909/1 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 688.21423497909 as a fraction:
9635/14 / 1