Your child may be considered a slow learner, but that does not make them a no-learner. There are things you can do to encourage your child that will help prevent them from giving up on learning out of frustration.
Not every attempt is going to result in success. Make it a habit to praise your child for trying. By encouraging the attempt to succeed, you let the child know that it is important to try, for success will never come if they don't.
Believe in your child's ability. Show your child that you are confident that they can succeed. By consistently expressing your confidence in their ability, they will learn to have confidence in themselves.
Rather than thinking of a failed attempt as the overall failure, teach your child that success often does not come without failure. Treat unsuccessful attempts as lessons in what does not work and help them think about what can be done differently the next time to increase the chances of succeeding.
Give your child examples of successful people who kept trying and finally succeeded. Stories of the Wright Brothers, Thomas Edison and others will show them that even the greatest accomplishments required hard work and many attempts.
Your child may be doing fractions, but that does not mean they have learned the basics of how to multiply or even add. Don't assume they have already mastered one skill simply because they have been asked to do the next one.
Work with your slow learner patiently and celebrate their every small success to encourage them.