Samuel bought 30 books. the hardcover books cost 20 dollars while the paper back books cost 8 dollars. if the total amount of books costed 480 dollars, how many passer back books were purchased?

White shapes and black shapes are used in a game. some of the shapes are circles. while the rest are squares. the ratio of the number of white shapes to the number of black shapes is 5: 11. the ratio of the number of white cicrles to the number of white squares is 3: 7. the ratio of the number of black circles to the number of black squres is 3: 8. work out what fraction of all the shapes are circles.