Guess the B'Day

Logic Level 3

Miss Jas, a teacher whose birthday is M/D (where M is month, D is day) has two students, Joy and Wen. Both students know that Miss Jas' birthday is one of the following:
2/15, 2/20,
4/14, 4/15, 4/18,
6/14, 6/17,
8/2, 8/18, 8/20
Miss Jas told M to Joy and told D to Wen. She then asked the two students the question, "Do you know what my birthday date is?"

Joy says: "If I do not know, Wen does not know it either".
Wen says: "I didn’t know it at first, but now I know".
Joy says: "Oh, then I know it too now".

So what is Miss Jas' birthday date?

Image credit: Wikipedia Twice25 .
02/20 04/14 04/18 06/14

View wiki
Vineet Prakash by Vineet Prakash , 34, India

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Firstly,John has no chance to know the birthday only with his number because every month has multiple dates. But Wen had a chance to know the b'day just by his number because 17 and 2 are the dates that don't have multiple months.So, when John says if he doesn't know(which is obviously true),Wen also doesn't know, it defines that the M's are not 6 or 8 so he is sure that the D's are never 17 or 2. (We have eliminated June and August :D ) Now,Wen has got idea that the M is either 2 or 4. He knows the D. If it would be 15,then he would be still confused. So it is either 20 or 14 or 18. Now,if the D would be 14 or 18,then John wouldn't be able to know the date cause both are of M=4 (which is the info he has) But as he has said that he has known it finally,so it is 20. AND THE DATE IS 02/20.

13 Helpful 0 Interesting 0 Brilliant 0 Confused

great solution !!!!!!!!!!!

PUSHPESH KUMAR - 6 years, 11 months ago

I am confused about the "when John says if he doesn't know(which is obviously true),Wen also doesn't know, it defines that the M's are not 6 or 8 so he is sure that the D's are never 17 or 2" I mean John (it should be joy btw) basically say wen doesn't know right? Since he doesn't know himself. So he say D isn't 2 or 17...and how would he know that? If John knows what D is or isn't he would already know the answer to the question!. Also you can eliminate June but August too? August still have 2 dates left so why do you cross it out?

Narisa Thamveerapong - 6 years, 11 months ago

Log in to reply

John doesn't know the date, but he saw that it is in february or april as he knows the M... that's why he gets the opportunity to say that wen must be confused. If it would be june or august,then wen had a probability to have that 17 or 2 D.

Md. Mohaiminul Islam - 6 years, 11 months ago
Benny Zhang
Apr 29, 2015

To be honest this question seemed like a knock off version of Cheryl's Birthday problem (from Singapore). In this problem, it states the exact same thing but the dates are different:

Albert and Bernard had just made friends with Cheryl, and they want to know what Cheryl's birthday is. Cheryl gives them a list of 10 possible dates:

May:15,16,19 June:17,18 July:14,16 August:14,15,17

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

Albert: I don't know what Cheryl's Birthday is, but I know that Bernard also doesn't know Bernard: At first I didn't know what Cheryl's Birthday is but now I know Albert: Then I also know

However, this problem actually has two answers depending on your perspective of how you interpret what the first statement is saying. Here are the two answers explained in this video. (url) https://www.youtube.com/watch?v=w3Nzkae_TRU

2 Helpful 0 Interesting 0 Brilliant 0 Confused

Hey! can you please check the dates the 2 and post it. And tell which was first one. I need to know badly

Nilesh Chouhan - 6 years, 1 month ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...