if 5 dice are thrown find the probability that at least 3 of them will turn up 6

so you want:

prob(3 turn up 6) + prob(4 turn up 6) +prob(all 5 turn up 6)
= C(5,3) (1/6)^3 (5/6)^2 + C(5,4)(1/6)^4 (5/6) + C(5,5)(1/6)^5 (5/6)^0
= ...