1. ## probability #2

another one..

25% of all students at the high school wears glasses. you randomly chose 15 students. what is the possibility that 7 or more of these students wears glasses?

2. You should consider the binomial theorem

Where n is number of trials, p is the probabilty of success and k is the required amount.

$\displaystyle P(X=k) = \binom{n}{k}p^k(1-p)^{n-k}$

In your case $\displaystyle n = 15$ and $\displaystyle p = 0.25$

Choose $\displaystyle k \geq 7$

$\displaystyle P(X\geq 7) = P(X= 7)+P(X= 8)+\dots +P(X= 14)+P(X= 15)$

3. Originally Posted by pickslides
You should consider the binomial theorem

Where n is number of trials, p is the probabilty of success and k is the required amount.

$\displaystyle P(X=k) = \binom{n}{k}p^k(1-p)^{n-k}$

In your case $\displaystyle n = 15$ and $\displaystyle p = 0.25$

Choose $\displaystyle k \geq 7$

$\displaystyle P(X\geq 7) = P(X= 7)+P(X= 8)+\dots +P(X= 14)+P(X= 15)$
This will be true as long as the number of students at the Highschool is 'large'.