Three chemistry students measured the length of a copper bar. the recorded lengths were 5.05 cm, 5 cm , and 5.1 cm, what is the average length of the bar by showing my work ?

I'm learning about the periodic tables and what each subject's configuration is. for example, hydrogen is 1s^1, but i don't understand how you get that. can someone me understand how to figure out how to figure this out? sorry if the question makes no sense, but it would really a lot if you could me understand! you so much if you can!