Four coins

If you were to toss four coins, what are the odds in favor of at least two landing heads up?

What is the sample space of four coins being tossed:

HHHH, HHHT, HHTH, HTHH, THHH. . .etc. Now of those how many have at least two H's in them?

Or, if you have studied the binomial formula, you recognize this as a binomial distribution with four independent trials (the individual coins being tossed).

Let X be the probability of tossing heads

Then