What is the probability that if 15 letters are typed, no letters are repeated?

What is the probability that a hand of 6 cards contains 6 cards of 6 different ranks?

A jar contains 6 red marbles, 7 green marbles, and 6 blue marbles. What is the probability that you draw 4 green marbles in a row if you do replace the marbles after each draw? =  What is the probability that you draw 6 blue marbles in a row if you don'™t replace the marbles after each draw? =

What is the probability that when three coins are flipped, two lands heads? Type your answer as a fraction