Answer
The probability that each of 1, 2, 4, 5, 6, is rolled is 1/7, and the probability of 3 is 2/7.
Work Step by Step
Let $p_i$ denote the probability that $i$ is rolled. We are given that $p_3 = 2p_1$, for instance. Then since $p_1 + p_2 + p_3 + \cdots + p_6 = 1$, we have $p_1 + p_1 + 2p_1 + p_1 + p_1 + p_1 = 1$, i.e. $7p_1 = 1$ and thus $p_1 = 1/7$.
So the probability that each of 1, 2, 4, 5, 6, is rolled is 1/7, and the probability of 3 is 2/7.
