Suppose the probability that an individual suffers an adverse reaction from a particular drug is known to be \(0.001\). The probability that out of \(2000\) individuals, exactly three will suffer an adverse reaction is ____.
Show Hint
Use Poisson approximation to Binomial when
\[
\boxed{
n\ge20,\quad p\le0.05,\quad \lambda=np.
}
\]
Then,
\[
\boxed{
P(X=r)=\frac{e^{-\lambda}\lambda^r}{r!}.
}
\]