## Algebra and Trigonometry 10th Edition

$$\frac{365\cdot364\cdot363\cdot362}{365^4}$$
Whenever one person has a birthday, there is one less day in the year that could be a different birthday. Thus, we multiply 365/365 by 364/365. We continue this trend for the given number of people that there are. So, for four people, we find: $$\frac{365\cdot364\cdot363\cdot362}{365^4}$$