# A teacher thinks of two consecutive numbers in the range 1 to 10, and tells Alex one of the numbers and Sam the other. Sam and Alex have the following conversation: Alex: I don't know your number. Sam: I don't know your number, either. Alex: Now I know! Can you find all 4 solutions?

1
by juttuc4

2015-05-06T19:53:46+05:30

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Two numbers are consecutive between 1 and 10.

If Alex or Sam were told  1 or 10,  then they would know the other number, as they would be just 2 or 9 respectively.  Hence, the numbers they are told are from :  2,3,4,5,6,7,8,9 .

Suppose  Alex had 2.. then Sam could be having 1 or 3...   Sam had  replied that he did not know what Alex had "either"...  If Sam had  1,  then  he would know what Alex had.  So  Sam would have 3 in that case.    One possible solution is  Alex = 2,  Sam = 3)

Similarly,  (9, 8)  pair is possible.  As, the person who is told 9, will guess that the other has 8,  after the 2nd line of conversation.

Suppose,  Alex had 3,  then Sam may have 2  or 4..  If Sam had 2, then he would know at the end of the second line of conversation that Alex had 3.  But he said, he did not know "either".. It means Sam could have only 4.  Thus  Alex = 3, Sam = 4.  is another possible solution.

Similarly,  if Alex had 8, then Sam could possess 9,, in which case Sam would claim that Alex had 8..  But Sam did not know "either".  So Sam did not possess 9.  So sam could have only 7.
So  (Alex 8, Sam 7) is another solution.

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If Alex is told 4, 5, 6, 7  then he would not know  even at the end of the conversation.  But in our conversation, Alex knew the solution at the end.  Hence,  the above mentioned 4 solutions are applicable.

That is the teach told Alex and Sam:  (2, 3) , (3,4) (8, 7) or (9,8) repectively.
For other combinations not involving 1 or 10,  it is not possible for Alex to Guess at the end of the conversation.

click on thanks blue button above please
why alex would not had known if he was given 4,5,6,7?
and can u tell me why are we considering the numbers one after the other in case: 2nd statement Sam: I don't know your number, either.: you had assumed only if 2 would be the next number.(in series order) .could you tell me why had you chosen in series (one after the other form)?