Learning to add and subtract has never been this easy! Level 3: Sums 13 to 20 Adding and subtracting basic equations by sight is essential to a solid math foundation. Meet the Math Facts 1, 2, and 3 make learning to add and subtract fun and easy! With adorable characters that your child will grow to love, your child will be able to easily recall basic math facts to 10 + 10. Preschool Prep Series products have won over 25 national awards and are used in thousands of schools across the country! You will be amazed at how easily your little one can learn math!