Sylvester and Erin collect baseball cards. Sylvester has 250 baseball cards and collects 15 cards per week. Erin has 300 baseball cards and collects 10 cards per week. After how many weeks will Sylvester and Erin have the same number of baseball cards? Write and solve an equation to model the problem. Explain the meaning of the solution.

Quick! a survey of 57 customers was taken at a bookstore regarding the types of books purchased. the survey found that 33 customers purchased mysteries, 25 purchased science fiction, 18 purchased romance novels, 12 purchased mysteries and science fiction, 9 purchased mysteries and romance novels, 6 purchased science fiction and romance novels, and 2 purchased all three types of books. a) how many of the customers surveyed purchased only mysteries? b) how many purchased mysteries and science fiction, but not romance novels? c) how many purchased mysteries or science fiction? d) how many purchased mysteries or science fiction, but not romance novels? e) how many purchased exactly two types of books?