There are 90 students in the school band. 30% of them are sixth graders, 40% are seventh graders, and the rest are eighth graders. How many band members are 6th graders?

Cam bought some used books for $4.95. he paid $0.50 each for some books and $0.35 each for the others. he bought fewer than 8 books at each price. how many books did cam buy?

How many $20 bills do you need to have to make $280

The figures below are made out of circles, semicircles, quarter circles, and a square. find the area and the perimeter of each figure and give your answers as a completely simplified exact value in terms of π (no approximations).