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jmc

counting and probability junior

Problem

An integer between and , inclusive, is chosen at random. What is the probability that it is an odd integer whose digits are all distinct?
(A)
(B)
(C)
(D)
Solution
There are options for the last digit as the integer must be odd. The first digit now has options left (it can't be or the same as the last digit). The second digit also has options left (it can't be the same as the first or last digit). Finally, the third digit has options (it can't be the same as the three digits that are already chosen). Since there are total integers, our answer is
Final answer
B