# What is the probability of this?.

A company has 100 employees, and the average time an employee stays in the company is 3 years.

A new employee starts to work, and he observes that in the first month 3 other employees stopped working at the company.

Now, what is the chance of this happening? should be considered a normal occurrence? or this event is rare?.

• Can we assume the time for an employee to stay in the company to be an exponential distribution with mean $1/\lambda = 3$ year ? – Zubzub Aug 14 '16 at 13:39
• Do the company still hire people on a regular basis such that the company retains an expected size of 100 employees? – Frenzy Li Aug 14 '16 at 13:40
• Yes, that number is a constant, when someone leaves the company another employee takes the position. – Artemix Aug 15 '16 at 7:43

## 1 Answer

If the company hires people uniformly then one can expect that in 3 years 100 people leave the company then each month $100/3 = 2.7$ people leave company. So in 3 month one would expect $2.7\times 3 = 8.1$ people to leave the company. So it is very little chance to only 3 people leave in 3 month.

• Yes I edited my answer but still the question needs more information in order to come with an exact answer. – Alithewise Aug 14 '16 at 14:46