Get them to have the same number on the bottom by finding the lowest common number when multiplying which would be multiplying them by each other by you also have to multiply the top number so for 1/5 multiply 1 & 5 by 3 and you get 3/15 then the same for 1/3 but multiply by 5 so it'll be 5/15 add them and you get 8/15 so you have 7/15 left.
