# How do you calculate the probability that three people will all win a prize in two consecutive weekly raffles?

My company is having a series of holiday raffles. Employees earn entries by completing specified tasks, so any employee may have one or more entries within a given week. We do not know how many entries there are in total, but we can see how many entries any given employee has submitted in each time period.

After two weeks, three employees have won twice. Some people (meaning "those of us who haven't won") are curious about the probability that this could happen.

If we assume that there are 2000 total entries and 1000 employees have entered in each of the raffles and there are 10 prizes in each raffle, how do we calculate the probabilty that

1 person wins twice

2 people win twice

3 people win twice

Relevance

If there are 2000 total, and 1000 employees then each employee should've entered about 2, but each two has a chance of one of the ten so you get 20/2000. Simplify to 1/100. That's for one person, once. To win again they must get 1/100 again, so they have 1/10,000 For two people you have 1/100 X 1/100 for one person & 1/100 X 1/100 for the second person so it would be 1/100,000,000 for two people. Three people would do the same thing; 1/100 X 1/100 X 1/100 X 1/100 X 1/100 X 1/100 = 1/100,000,000,000,000. So if three (same) people win two in a row, it would be extremely rare.