So when is Cheryl’s birthday?

(James Higginson) #1

This was an actual problem set to 14-year-olds in the Singapore and Asean Schools Math Olympiads (SASMO)

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?


(Billy Gibson) #2

(Billy Gibson) #3

(Nick Ord) #4

Thanks Terry

(Terry Williams) #5

You'll find the explanation here, Nick. Be warned, it's as complex as the question!

(Nick Ord) #6


(Peter Bird) #7

It's a process of elimination Nico, you whittle away at what it can't be.

(Bruce Brewer) #8

Think it's a fib....does anybody know a Singaporean called Albert and Bernard or Cheryl?

(Nick Ord) #9

So mathematically, what is the process - I can't get it - but then - I'm thick

(Peter Bird) #10

Easy peasy - you share your birthday with Lorraine Chase of Luton Airport fame.

By coincidence my big brother was married on this day in 1966 slap bang in the middle of the World Cup when England were playing Mexico, trust him tho' it didn't stop me finding the tv lounge during the reception !

(Terry Williams) #11

I share my birthday with Cheryl, if that helps!

(Sarah Hague) #12

I didn't understand the explication when I read it... and just thought that Cheryl sounded like a lot of hard work as a friend.

(Rachael Fillatre) #13

Too much for my brain ! ;-)

(Paul Punchard) #14

I make it July 16th