Knowledge retention was only capped at 5 years in the 2000, based on what my diploma lecturer shared with my cohort. And now, while I am upskilling the knowledge retention is as good as less than 2 years, as shared by my lecturers. Life is constantly a need for continuous learning. Maybe your degree in maths will help you in years or months ahead. Sometimes we don't understand what benefit it brought along, but there will always be something worth it.