so when you  want to find the closest  number to something you find the difference between the number and the other number that you are given you could times divide add etc but you have to use the method in the right way so your trying to find 500 from 450 so you could add 50 to get their but their is another number 510 so  you could easly do  510-10=500 that  was my guide  how to find the difference between 2 numbers