Factorize into prime factors the numerators and denominators of the reduced fractions.
The end fraction will have as the numerator the product of all the numerators' prime factors and as the denominator the product of the denominators' prime factors.
Reduce all the common prime factors that appear in the end fraction's both factorized nominator and denominator.
Perform effectively the multiplying operations of the remaining prime factors above the fraction line, for the numerator, and under the line, for the denominator.
The end fraction cannot be reduced anymore, since all common prime factors were reduced previously.
If the case, if the fraction numerator is higher than the denominator (improper fraction), the end fraction could be written as a mixed fraction, consisting of an integer and a proper fraction.
An example of multiplying of ordinary fractions, with explanations
Let's multiply three ordinary fractions: 6/90 * 16/24 * 30/75.
Reduce each fraction to lower terms (simplify):
Factorize each fraction's both numerator and denominator into prime factors
Divide both the numerator and denominator of each fracton by the number containing only their common factors, at lowest powers - this is the greatest common factor GCF (greatest common divisor GCD) of each fraction's numerator and denominator