Each of four students chooses at random one integer from 1 to 10 inclusive. What is the probability that at least 2 of them choose the same integer?
Please help!
Do you understand that there are $\displaystyle 10^4$ ways to choose the integers?
Let's find the number of ways that no two of the same integers are chosen.
That number is $\displaystyle 10\cdot 9\cdot 8\cdot 7$. WHY?
Then what is the number in which at least two of the same are chosen?