Question

jan has a fair 20 sided polyhedron die, numbered 1 through 20. she rolls it 300 times

predict the approximate number of times jan expects to roll a number that is 18 or greater?

Answer 1

Probability of rolling 18, 19, or 20 = 3/20 = 0.15.
Expected count in 300 rolls = 300 × 0.15 = 45.

(If useful: SD = sqrt(300·0.15·0.85) ≈ 6.19, so a typical spread is about 45 ± 6.)