```
## Pass a vector to sum, and it will add the elements together.
sum(1:5)
## Pass several numbers to sum, and it also adds the elements.
sum(1, 2, 3, 4, 5)
## In fact, you can pass vectors into several arguments, and everything gets added.
sum(1:2, 3:5)
## If there are missing values, the sum is unknown, i.e., also missing, ....
sum(1:5, NA)
## ... unless we exclude missing values explicitly:
sum(1:5, NA, na.rm = TRUE)
```

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