yeah! i forgot to add "times"
would it me around 25% cause 1 extra chance right? with 1 more toss
The concepts involved in probability theory are quite simple; applying them is complex because it is so easy to forget something relevant.
First, please read Dr. Peterson’s wonderful answer.
Second, although it is frequently the hardest method computationally, I find that what is most intuitive for me is to think conceptually using the method that follows. If A and B are mutually exclusive, then the probability of A or B is just the sum of the probability of A and the probability of B. Note that this method will not work unless A and B are mutually exclusive, which means that the probability of A and B is zero, just plain impossible.
Third, you are of course correct that the probability of flipping a fair coin three times and getting three heads is
[math]\left (\dfrac{1}{2} \right )^3 = \dfrac{1}{8} = 12.5\%[/math].
So far, so good. However, it is unclear what you mean thereafter. Why do you add 25%, which would give a total of 37.5%? Or are you adding 12.5%, which would give a total of 25%? Let’s not worry too much about answering those questions because both answers are wrong.
Let’s try my method of thinking (while remembering it may not be the only way of thinking and may not be computationally efficient).
In what ways can I get at least three heads in a row with four flips?
3 heads then a tail.
A tail then 3 heads.
4 heads.
Are they mutually exclusive?
What are their respective probabilities?
So what is their sum?
Fourth, with a problem this small, you can
CHECK your answer by listing the sixteen possibilities and counting. Obviously that is not going to work with 10 flips. And as Dr. Peterson indicated, there is a complication with 10 flips that is rather trivial with 4 flips. So here is a hint.
Solve the problem for 5 flips. Use that answer to get the answer for 10 flips.
EDIT: I did not read Dr. Peterson’s answer carefully enough. I assumed that the question was “at least three heads in a row.” There is a reason why our guidelines say to give the problem completely and exactly.