SMO Junior · 11. Counting and probability
Count with a clear plan — multiply, add, glue, leave gaps, take the complement, choose, distribute — and turn counts into probabilities; finish hard cases with states and recursion.
Use the product and sum rules, blocks and gaps correctly.
Count with the complement and inclusion–exclusion.
Use combinations and stars and bars with bounds.
Compute probabilities from equally likely outcomes and expected values with states.
Set up recurrences and parity arguments for paths and sequences.