Basic arithmetic with two or more inputs

### User story
As an analytical code developer, I want a function that adds, subtracts, multiples or divides two or more numbers as specified by the user, so that I can practice using Git.

### Definition of done
- [ ] Runs without error
- [ ] Fully meets the user requirements
- [ ] Documented using a [docstring for python](https://peps.python.org/pep-0257/) or [roxygen2 comment for R](https://cran.r-project.org/web/packages/roxygen2/vignettes/roxygen2.html)
- [ ] Peer reviewed and updated if needed

No source file or test entry point is named. First inspect the repository to identify where the arithmetic function belongs and whether Python or R is intended; use the user story to determine the supported operations and multi-input behavior, then add the requested documentation and verify each requirement in the definition of done.

Written by the indexing model from the issue text.