Try making a copy of this spreadsheet to calculate the damage of an army of skeletons.
Just enter the parameters and all the dice rolls are randomly simulated, with advantage or disadvantage too.
https://docs.google.com/spreadsheets/d/13eKsQDgn4Bqx40VHNR9CVH6CeZUnRZ7-4zX4IM7gfyg/edit?usp=sharing