I will be graduating with my bachelor's degree in mechanical engineering, in a few months, but I want to pursue master's in mathematics after 2-3 years. To prepare, I am currently doing "Advanced Engineering Mathematics" by kreyszig but wanted to do some additional stuff alongside, after thinking, I boiled down my options to following two categories; either I can do some mathematics project involving various mathematical topics intermixing or I can work on some open-ended problem in mathematics giving me an in depth understanding of the field. In addition, my area of interest in mathematics is primarily probability & statistics and numerical analysis but I am open to other fields in mathematics having weak correlation to the above mentioned areas too. I need help in deciding which approach will be best for learning mathematics alongside helping me prepare for my master's in mathematics with some solid work.
Thanks in advance