the answer is 50%
if you list out the possibilities, you get
(H being heads, T being tails)
HHH <- 3 heads
HHT <- 2 heads
HTH <- 2 heads
HTT
THH <- 2 heads
THT
TTH
TTT
we counted 4 of them to have at least 2 heads out of the 8 possibilities
4/8 = 1/2 which is 50%