A 20 lb bag of nut mix has 40% of peanuts and 60% of cashews. To get 20% peanuts, how much of the mix should be replaced with pure cashews?

remove 20% of peanuts and add 20% to the cashews

subtract 20% from peanuts and add that to cashews and you have 20% peanuts and 80% cashews. so you add and get 100%.