Final answer:
Kate originally has 2 books and ends up with 9 books after purchasing more. By subtracting the original amount from the total, we find that Kate buys 7 books.
Step-by-step explanation:
The question asks us to determine how many books Kate buys if she starts with 2 books and then has a total of 9 books after her purchase. This is a simple subtraction problem, part of elementary arithmetic, which is often taught in middle school mathematics classes.
To find out how many books Kate bought, we subtract the number of books she originally had from the total number of books she has after her purchase:
Total books after purchase - Original number of books = Number of books bought
9 books (after purchase) - 2 books (originally) = 7 books bought
Thus, Kate buys 7 books.