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# Permutations and Combinations (Metric)

Learn, or revise, permutations and combinations, an the binomial theorem.

## Units

### Permutations and Combinations

The number of permutations of $$r$$ objects from $$n$$, and the number of choices of $$r$$ objects from $$n$$.

The expansion of $$(a+b)^n$$ for positive integer $$n$$.