-- All of the non-zero digits are: 1, 2, 3, 4, 5, 6, 7, 8, and 9 .
that's nine digits all together.
-- The odd ones are 1, 3, 5, 7, and 9 .
There are five odd ones.
-- The even ones are 2, 4, 6, and 8.
There are four of them.
-- Two odd digits are already used, and we can't repeat them.
So we have 7 choices left for the last digit ... 3 odds and 4 evens.
-- Probability = (number of successful choices) / (total possibilities)
Successful choices . . . an odd digit, 3 available
Total possibilities . . . 7 unused digits
Probability = 3/7 (choice C)
