My team send this IQ test to me:

```
Albert and Bernard just became friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates.
May 15, May 16, May 19
June 17, June 18
July 14, July 16
August 14, August 15, August 17

Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.

Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too.

Bernard: At first I don’t know when Cheryl’s birthday is, but I know now.

Albert: Then I also know when Cheryl’s birthday is.

So when is Cheryl’s birthday?

```

My answer is `Aug 17th`

Here is why:

1. I assume the statment from A and B are true (obviously it can be a mistake).
2. I assme C is not a stupid girl.

### Step 1
The answer must not be May 19, June 18.

Otherwise B can get the answer easily.

May 15, May 16, ~~May 19~~

June 17, ~~June 18~~

July 14, July 16

August 14, August 15, August 17

### Step 2

Since A said he sure B don't know the answer (same as my first guess).

The month should NOT be June.

Otherwise, A will get the answer June 17.

Now only:

May 15, May 16, ~~May 19~~

~~June 17~~, ~~June 18~~

July 14, July 16

August 14, August 15, August 17


### Now interesting


May 15, May 16

July 14, July 16

August 14, August 15, August 17

As B heard A said: `I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too.`

The only possible date is `August 17`, as he only get `17`
So that can he say: `At first I don’t know when Cheryl’s birthday is, but I know now.`