what is the probability of gettin heads three time in a row on the toss of a coin?

Assuming you mean tossing the coin three times.

For a fair coin the probability is 1/8.

Each toss has a 1/2 probability coming up heads. Since these are independent events you multiply the probabilities together:

1/2 * 1/2 * 1/2 = 1/8

I like the above answer but this is an independent trial. The odds are 50/50 each and every time. I assume, however, that probability is the key.

The key to this is how you begin: If you start with tails facing up it will land on heads ..........Try it three times..........I wonder how many people are going to try that now !