Marianne buys 16 bags of potting soil that comes in 5/8- pound bags. If marianne's father calls and says he needs 13 pounds of potting soli, how many additional bags should she buy?
Say . . . (13 lbs)/(5/8 lbs/bag) . . . make sure units cancel . . . 13/5*8 = 20.8 bags . . . but get 21 bags just because you can't buy a fraction of a bag.