Answer
a) 12 options
b) $5/6$
c) $1/3$
Work Step by Step
a) $4 * 3 = 12$ (4 first digit options * 3 second digit options)
b) The possible options are as follows: $12, 13, 15, 21, 23, 25, 31, 32, 35, 51, 52,$ and $53$. Of these options, 10 have either a 2 or a 5.
$10/12$
c) $13, 23, 31,$ and $53$ are prime, so there are four options out of twelve. $4/12 = 1/3$
