You had dinner in a restaurant and the bill was $17.25. You gave the waitress $20 and told her to keep the change. What percentage of the bill was her tip?

Last month, a 770 g box of cereal was sold at a grocery store for $3.10. however, this month, the cereal manufacturer launched the same cereal in a 640 g box, which is being sold at $2.50. what is the percent change in the unit price?