+318 The parents of the students at Amelia School decided to buy new books for the school's library. The librarian gave them a list of books that were needed along with the price of each book. The parents chose 75 books. 15 of the books cost $16.21 each, 14 cost $25.10 each, 16 cost $20.70 each, and the rest of books cost $38.59 each. How much did the parents spend in all?
The first step to solving this problem is to figure out how many types of books there are, and how many books are in each type.
Here, I've listed each book type as a variable, so it will be easier to add them all up in the end.
x = 16.21 (15 of these)
y = 25.10 (14 of these)
z = 20.70 (16 of these)
r = 38.59 (variable number of these)
We know that there are 75 books in total, so once you subtract the number of each type of book from 75, you get:
75 - 15 - 14 - 16 = 30
This means that there are 30 of r books.
Now, we can multiply each of the costs by the number of books.
15x = 16.21*15
14y = 25.10*14
16z = 20.70*16
30r = 38.59*30
From this, we get:
xcost = 243.15
ycost = 351.40
zcost = 331.20
rcost = 1157.70
Now, we can add all of the numbers together to get:
243.15+351.4+331.2+1157.70 = 2083.45
(Hopefully this is correct!) 
