Let 4x be the number of books Peter borrowed initially and 5x be the number of books John borrowed initially.
The books left after returning 7 books each are (4x - 7) and (5x - 7).
The ratio of the books left is (4x - 7):(5x - 7) = 1:3
3(4x - 7) = 1(5x - 7)
12x - 21 = 5x - 7
12x - 5x = -7 + 21
7x = 14
x = <<2=2>>2
The number of books John borrowed initially is 5(2) = <<5*2=10>>10. Answer: \boxed{10}.
Peter and John borrowed books in the ratio of 4:5. After they returned 7 books each, the ratio became 1:3. How many books did John borrow at first?
1 answer