For this problem, 85% of people wear their mask while working. If there are 9 people working, what is the probability that at least 2 people are NOT wearing their mask?
From my understanding, this is finding $P( k \geq 2)$. I know need to use the a value $p=.15$. Based off notes, I should sum all probabilities for $k=2, 3, 4, ..., 9$.
However, I'm led to believe that $P(k \geq 2)$ is the same as $Q(k \leq 1)$.
NOTE: $P$ denotes the total probability where $p=.15$, $Q$ denotes the total probability where $p=.85$
Either way, I'm not getting the desired answer, which should be $=.4005$.
I plugged in my values into this calculator, with the values being: Probability of success on a single trial = $.15$, number of trials = $9$, and number of successes $= 2$, and it showed the cumulative probability $P(k \geq 2) = .4005$.
Is my understanding of the question/approach incorrect? What am I doing wrong?