P(E) = desired ÷ total
0 = impossible 1 = certain
AND × OR +
List every equally-likely outcome
2 coins = 4 · 3 coins = 8 · 2 dice = 36
Multiply the options at each stage
3 × 4 × 2 × 3 = 72
A fixed choice counts as 1.
Multiply ALONG a path
Add BETWEEN paths
“At least one” = add the paths that have it
= result ÷ trials
Estimates probability from real results
All rel. freqs add to 1