The waiter in charge of the Mechelsestraat pizzeria systematically under-
reports the amount of tips he receives from customers: in fact, for every
n customer that pays a tip he only reports n − m tips back to Tito.
Finally, Tito decides to confront the waiters by dining (and tipping!)
there incognito once a day for n days. What are the chances that 3 of
Tito’s tips go unreported by the waiter if n = 100 and m = 10?
Hint: ln n! = n ln n − n + O(ln(n))

请问这个题目怎么做啊？