Saturday, January 28, 2012

A REAL REAL Number Puzzle

Okay so here's a good one in order to make up for that last one.

A teacher thinks of two consecutive numbers between 1 and 10. The first student knows one number and the second student knows the second number. The following exchange takes place:
First: I do not know your number.
Second: Neither do I know your number.
First: Now I know.
What are the 4 possible solutions?

11 comments:

Caleb said...

So, the lying first student doesn't actually know, he just knows four possibilities?

Luke Murphy said...

Neither of the students are lying. The first student knows both numbers, but WE only know that there are 4 possibilities.

Dad said...

Huh? Both numbers? Am I wrong in assuming that the solution is four pairs of numbers between 1 and 10 and each pair is consecutive?

Dad said...

Do the students know that the numbers are consecutive?

Luke Murphy said...

Yes, they know that the numbers are consecutive.

Luke Murphy said...

So if the first student's number is 5, then he knows that the second student's number is either 4 or 6.

Luke Murphy said...

The first student, at the end of the exchange, knows both numbers exactly. From this, you and I can deduce 4 different possible pairs.

Dad said...

Got it.

Luke Murphy said...

Anna wants everyone to know that she got it first, this afternoon. I couldn't post a comment then because the internet was down.

Dad said...

I had it yesterday morning but I'd just washed my hair.

Uncle Don. said...

I think that this puzzle is FUBAR.