1. ## 2 probability questions

I have just recently been learning probability and I have been having troubles with some questions. If someone can help me on these two question, I would appreciate it.

1. A basketball player has a success rate of 80% for shooting free throws. What is the probability she will make atleast three out of 5 attempts.

2. A person is chosen at random from shoppers at a store. If the person's probability of having blonde hair and glasses is 2/25 and the probability of wearing glasses is 9/25, determine P(blonde hair|wears glasses).
The only thing I could do is do a venn diagram for this question and I'm not too sure if it's even right. Please reply if you know how to do these two questions.

Thanks

2. Originally Posted by munkeyb0i

1. A basketball player has a success rate of 80% for shooting free throws. What is the probability she will make atleast three out of 5 attempts.
The probability of making the three shots and missing the other two is:

$\displaystyle \frac{5!}{3!2!}0.8^3\times 0.2^2=\frac{5.4.3.2.1}{3.2.1\times2.1 }0.8^3\times 0.2^2\approx 0.205$

This is the probability of three successes in 5 attempts for a binomially
distributed random variable with probability of success on a single attempt of
$\displaystyle 0.8$.

Your notes/text book should provide a detailed explanation of why this is the
case.

RonL

3. Originally Posted by munkeyb0i
2. A person is chosen at random from shoppers at a store. If the person's probability of having blonde hair and glasses is 2/25 and the probability of wearing glasses is 9/25, determine P(blonde hair|wears glasses).
The only thing I could do is do a venn diagram for this question and I'm not too sure if it's even right.
P(blond and glassess)=P(blong|glasses)P(glasses)

so:

2/25=P(blond|glasses).9/25

hence:

P(blond|glasses)=2/25.25/9=2/9

RonL