Math
posted by Kay .
I form a 3digit number at random from the digits 19. What is the probability that my number has no repeated digits? All three digits the same? Exactly one repeated digit?

please?

number of cases with no repeating digits
= 9x8x7 = 504
number of cases where digits repeat
= 9x9x9 = 729
so prob(no repeating digits) = 504/729 = 56/81
all 3 digits repeat, could be 111 , 222, .. 999
or 9 of them
prob = 9/729 = 1/81
I am not clear what you mean by "exactly one repeated digit" 
one digit is repeated twice