all possible outcomes on 3 coins are: 3 heads: HHH --> 1 outcome 2 heads: HHT or HTH or THH --> 3 outcomes 1 head: HTT or THT or TTH --> 3 outcomes 0 heads: TTT --> 1 outcome

Question asks for at least 1 head which is any of the top 7 outcomes.

Now each of these outcomes has a probability of (1/2)*(1/2)*(1/2) --> 1/8 since we have 3 coins flipped at a time.

So the answer is 7/8. In other words, it is highly likely to get at least one head when flipping 3 coins. The only time you would not is by getting 3 tails.