(c) $\dfrac{5}{6}$
Total outcomes = 6. Favourable outcomes (numbers other than 3) = {1, 2, 4, 5, 6} = 5. So P = $\dfrac{5}{6}$.
The examiners expect you to identify the favourable outcomes (all numbers except 3) and apply the formula P(E) = favourable outcomes ÷ total outcomes. Alternatively, P(not 3) = 1 − P(3) = 1 − 1/6 = 5/6 using complementary events.