Simply do mental calculating. Sudoku, other math challenges. I had a workbook on construction math that had a wide variety of challenging problems.

As stated in my old post, I played Free Cell and Minesweeper. Free Cell requires multiple step processing. Minesweeper requires recognizing and memorizing patterns.

Go grocery shopping and add up the items as you take them from the shelf. Practice calculating unit cost. $1.20 for 18 oz. How much per oz?

Practice. Neuroplasticity is just the ability of the brain to change. It is not locked into any injury form. With effort, it can be re-energized to do many things. It requires practice, practice and more practice.

You could do some free exercises at Brain Exercises, Brain Training, Brain Health – BrainHQ from Posit Science or Lumosity or other Brain training games.

If you struggled for A's this past year, get the text book and do all the work again over the summer.

Do Khan Academy. https://www.khanacademy.org/math

Challenge your brain to succeed rather than look for confirmation that you will fail.

Put you smart phone away unless if can be used to challenge you will math. Otherwise, smart phones tend to enable simplistic thinking.