Mean Statistics
https://www.cuemath.com/data/harmonic-mean/
https://www.mathsisfun.com/numbers/harmonic-mean.html
Creating a function for lists and global variables
https://betterprogramming.pub/python-user-defined-functions-65f8662e2528
https://www.codecademy.com/forum_questions/52ba0f8780ff337a040035ca