Answer
$$A = \{ 134, 135, 136, 234, 235, 236 \}$$
Work Step by Step
1. Write the sample space:
$S = \{123,124,125,126, 134, 135,136,145,146,234,235,236,245,246,256,345,346, 356, 456 \}$
If 3 is the second smallest, there must be a 2 or a 1 in the outcome, so 3 is not the smallest one, so we eliminate 345,346,356 and 456.
Since it can't be the larger number, there must be a 4, 5 or 6, so we eliminate 123.
And most important, there has to be a "3" in the outcome, so we eliminate: 124,125,126,145,146,245,246 and 256.
$$A = \{ 134, 135, 136, 234, 235, 236 \}$$
