Art, Ben and Cam are sitting at a table.
On the table are 10 cards:
3 blue cards numbered 2, 3 and 6
2 green cards numbered 4 and 5
2 red cards numbered 1 and 3
3 white cards numbered 1, 2 and 4

I have one of those cards in mind says Cam;
I'll tell Art the color and Ben the number.
Cam does so...secretly of course.

Ok says Cam, can you figure out my card?

Art: I don't know, but I know that Ben doesn't either.

Ben: I didn't know, but now I know.

Art: I now also know.

What was Cam's card?

Denis, did you find this one in Singapore?

Yes...liked it so much I rewrote it....shhhh

After Art's reply, Ben knows the card is red or white.
(It can't be blue since Cam could have told him the card
was a 6. It can't be green since Cam could have told him
the card was a 5. In either case, Art could not have
replied with certainty that Ben doesn't know.)

After Ben replies that he knows the card, Art knows the card
is a red 3. (It can't be 1, 2, or 4 since Ben could not have
replied with certainty that he knew the card.)

Yepper CC!

If ya'll wanna see it in detail,
change colors to May(blue),Jun(green),Jul(red) and Aug(white),
and numbers 1 to 6 to 14 to 19, and go here:
http://www.bhavinionline.com/2015/04/viral-riddle-when-is-cheryls-birthday/

I had to laugh when I first saw this one because it's so close. They were off by one day, though. My birthday is July 15th!

Is that right! Mine's July 22nd.
You're a week older than me...