Coco flips a penny, a nickel, and a quarter. Each coin is fair (meaning that heads and tails are equally likely to come up). What is the probability that at least two of the coins comes up heads?

The possibilites are: HHT, HTH, THH, HHH

= (1/2) x (1/2) x (1/2) = 1/8 for each of the four possibilities.

Adding together these possibilities: (1/8) + (1/8) + (1/8) + (1/8) = ....