Cross Factoring

When you are going to multiply or divide two fractions, if the numerator of one and the denominator of the other have a common factor, then you change those numbers to the number of times the factor goes into that part of the fraction (numerator or denominator.) Make sure to change both common numbers!

Ex.: in the problem 5/8 x 4/10 the numerator of 5/8 (5) and the denominator of 4/10 (10) have a common factor (5) and vice-versa so you can change the 5 in 5/8 to a 1 because 5 goes into 5 once and the 10 in 4/10 has to become a 2 because 5 goes into 10 twice.Your problem then becomes 1/8 x 4/2 you can do the same things with the 8 from 1/8 (it becomes a 2) and the 4 in 4/2 (it becomes a 1) your problem becomes 1/2 x 1/2 which equals 1/4 . If you hadn't cross factored you would have had to do 5/8 x 4/10 which equals 20/80 which eventually simplifies to 1/4 but it would take a lot longer!!!