
Question 1:
What is the probability of obtaining at least 2 successes before the 6th trial if the probability of success is 0.3 in each trial?
Answer 1:
Probability for success per trial is 0.3. Obtaining at least 2 successful trials is alternatively not obtaining 0 or 1 successful trials.
That’s the probability for that:

Question 2:
If a certain basketball player has a free throw percentage of 75%, what is the probability that he will make his first free throw on his 4th attempt?
Answer 2:
For this we need the Geometric distribution:

Question 3:
A certain coin has a probability of landing heads-up of 0.2. If the coin is flipped until the first head appears, what is the expected number of flips?

Answer 3:
For this we need to use the geometric probability again, and find the expected value for probability of success of 0.2.
There’s the calculation:

According to the calculation, it is expected that success will take place in the 5th time, that means, there will be 4 non-successful trials, and then the successful trial.