an unbiased coin is tossed 3 times. find the probability that the coin lands heads exactly once.

n = # of things to choose from and r = # that you choose.

5! = 5 factorial = 5*4*3*2*1 = 120

nCr = n!/r!(n-r)!

To find the probability of an event, we need to calculate the ratio of the number of desired outcomes to the total number of possible outcomes.

In this case, we have an unbiased coin that is tossed three times, and we want to find the probability that the coin lands heads exactly once.

Let's break down the possible outcomes:

1. Heads - Tails - Tails
2. Tails - Heads - Tails
3. Tails - Tails - Heads

There are three possible outcomes where the coin lands heads exactly once.

Now, let's determine the total number of possible outcomes when tossing a coin three times. Since each coin toss has two possible outcomes (heads or tails), the total number of possible outcomes is 2 * 2 * 2 = 8.

Therefore, the probability of the coin landing heads exactly once is 3/8.