I am having a difficult time with understanding and using equations for weighted means, variance and deviation.

I have a question that lists the hours worked and frequency of workers in a table.

Hours EmployeesI calculated the weighted mean (sum of all the hours times the frequency, divided by the total frequency).

12 1 32 5 35 7 38 8 42 5

I understand and correctly calculated 35.81 as the weighted mean. I'm not sure how to use this in order to find the standard deviation and variance.

I am struggling with it as a concept more so than I am struggling with numbers (if that makes sense).

*I may not understand certain math terms, as my learning has been messed up by moving to other countries, which required me to take earlier necessary courses, setting me back at least 1 grade level.