In order to continue calculating with numbers that are as small as possible, i.e., manageable, fractions should also be shortened as much as possible. This is achieved by dividing the numerator and the denominator of the fraction by their greatest common divisor (GCD)..
Example: Shortening with greatest common divisor
Based on the above example with the fraction 1040, the greatest common divisor of 10 and 40 is 10.
So you can shorten the fraction by 10 to get the fraction that cannot be shortened further. Then the numerator and denominator no longer have any common divisors except 1.