[ironrabbit]

I shouldn't have tried to fit that on one slide :)

Consider the case if the birthday is May 19th:

- Bernard knows the date, and he knows that May 19th is the only possible "19th", so he knows the answer immediately.

- Albert would know it's in May, and that May 19th is possible. So, he knows there's a chance that Bernard knows the birthday immediately.

Since in the question, Albert is confident that Bernard doesn't know the birthday immediately, we can conclude that the month cannot be May. The exact same logic applies for June and the 18th.

The only possible months are July and August, because every possible date in July and August also appears in another month.

Hope that makes more sense!