Let's assume you wanted to compare 4/5 to 3/4 to see which is larger?
set them equal to one another and then cross multiply like this
4/5 = 3/4 now cross multiply from bottom to top & write the number above the fraction like this
(4 x 4 = 16) (5 x 3 = 15)
4/5 = 3/4
Since 16 is larger than 15, 4/5 is larger than 3/4!