Jennifer earned $50 from her part time job. She wants to put $15 of her earnings into a savings account. She spends $24.99, including tax, on a new hardcover book, but also wants to buy some new bookmarks. If each bookmark costs $1.75, including tax, what is the maximum number of bookmarks she can buy?

Jennifer has earned a total of $50. She plans to put $15 into a savings account, which leaves her with:

\[ 50 - 15 = 35 \]

Next, Jennifer spends $24.99 on a hardcover book. Subtracting the cost of the book from her remaining amount gives:

\[ 35 - 24.99 = 10.01 \]

Now, she wants to buy bookmarks, which cost $1.75 each. To find out how many bookmarks she can buy with $10.01, we divide her remaining amount by the cost of one bookmark:

\[ \frac{10.01}{1.75} \approx 5.724 \]

Since she cannot buy a fraction of a bookmark, we take the integer part, which is 5. To ensure she can afford 5 bookmarks, we calculate the total cost for 5 bookmarks:

\[ 5 \times 1.75 = 8.75 \]

Now, we check if Jennifer can afford 5 bookmarks by seeing if she has at least $8.75 remaining:

\[ 10.01 - 8.75 = 1.26 \]

Since she does have enough money remaining after buying 5 bookmarks, we check the cost of 6 bookmarks:

\[ 6 \times 1.75 = 10.50 \]

In this case, $10.50 exceeds her remaining $10.01, confirming that she cannot afford 6 bookmarks.

Thus, the maximum number of bookmarks Jennifer can buy is:

\[ \boxed{5} \]