Step 1:
The first step to converting 2.1093749923845E-10 to a fraction is to re-write 2.1093749923845E-10 in the form p/q where p and q are both positive integers. To start with, 2.1093749923845E-10 can be written as simply 2.1093749923845E-10/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 2.1093749923845E-10, which in this case is 17. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 2.1093749923845E-10/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 2.1093749923845E-10/1 each by 100000000000000000:
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 2.1093749923845E-10 as a fraction:
1/4740740757 / 1