Binomial Distribution Problem Involving Excel

Question

Here's the question: 7% of the American population has O-negative blood. if 10 people randomly donate blood, what is the probability that at least 1 of them has O-negative blood? (Round to 3 decimal places)

Here's the excel formula I used to solve it:

=BINOM.DIST(1,10,0.07,FALSE)

I got 0.387420489 as my answer, but it's incorrect. What am I doing wrong?

Answer 1

The correct answer is equivalent to not having all ten not O-negative, i.e. $1-(1-0.07)^{10} \approx 0.516$. Any of the following Excel formulae will give this:

=1-(1-0.07)^10

=1-BINOM.DIST(0,10,0.07,TRUE)

=1-BINOM.DIST(0,10,0.07,FALSE)

=1-BINOM.DIST(10,10,0.93,FALSE)

=BINOM.DIST(9,10,0.93,TRUE)