Answer to Question #181511 in Statistics and Probability for Vinnakota Chandra Sekhar

Question

A fair die is rolled till all the numbers 1, 2, ..., 6 appear on the top. What is the probability that at least 7 rolls are needed?

Answer 1

$\frac{6\times6!+15\times6!}{6^7} = \frac{21\times6!}{6^7} = 0.054 =$ 5.4%