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