I answered a similar problem yesterday.
In three coin tosses there are 8 possible outcomes:
H H H
H H T
H T H
T H H
T T H
T H T
H T T
T T T
Of those results, four out of the eight have at least 2 tails and so the probability is (4/8) or50%
If you need the probability of getting EXACTLY 2 tails then the probability is (3/8) or .375