Final answer:
To find the cost for 20 books on sale for 4 for $10.00, divide $10.00 by 4 to find the cost per book, then multiply that cost by the number of books to find the total cost.
Step-by-step explanation:
To find the cost for 20 books, we need to determine the cost for each book. Since the bookstore is selling 4 books for $10.00, we can divide $10.00 by 4 to find the cost per book. $10.00 divided by 4 is $2.50. So, each book costs $2.50.
Now, we can multiply the cost per book by the number of books we want to find the total cost. In this case, we want to find the cost for 20 books. So, we multiply $2.50 by 20. $2.50 multiplied by 20 is $50.00. Therefore, the cost for 20 books is $50.00.