There are 5 shelves with 4 books on each shelf. Total number of books = 5 × 4 = 20 20 books 20 books 5 shelves 4 books on each shelf 4 books on each shelf 5 shelves 20 ÷ 5 = 4 20 ÷ 4 = 5 5 × 4 = 20