Question

Jose has a comic book collection that he keeps among 5 shelves with a equal number on each shelf. His father adds 20 books to the bottom shelf, so the shelf now has 125 books. How many total books are in his collection? Use algebra to solve the equation

Answer 1

Let's say the number of books on each shelf before his father added more books was n.
The total number of books on that shelf added by his father is n+20 books.
There were initially n books on each of the 5 shelves, so the first four shelves had 4*n books.
There were 4*n books on the first four shelves, and since the bottom shelf had n+20 books, the total number of books in the collection is 4n+n+20=125 books.
Combining like terms gives 5n+20=125.
Subtracting 20 from both sides gives 5n=105.
Dividing both sides by 5 gives n=<<21=21>>21 books on each shelf.
If there are 21 books on each shelf, then the total number of books in the collection is 5 shelves * 21 books/shelf = <<5*21=105>>105 books. Answer: \boxed{105}.