Question: Your team wants to hire a new colleague. The team wants to interview at most $K$ persons, and candidates are interviewed one at a time. After each interview the team has to decide to hire or reject the candidate. How can your team maximize the probability of hiring the best candidate amongst $K$ persons?
Answer: first interview $R$ candidates and reject all. Then interview candidates until you find a candidate that is better than all of the first $R$ candidates. The number $R$ depends on the maximum number $K$ that you wish to interview.
For $K=5$, $R=2$
For $K=10$, $R=3$
For $K=100$, $R \approx \frac{K}{e}-1 \approx 36$.
This puzzle is known as the Secretary Problem; see the link for the exact formula to calculate $R$.
The solution also shows the disadvantage of interviewing candidates one at a time: the first $R$ candidates interviewed never have a chance to be hired as they become the benchmark to beat!
Source: Haigh.