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 William's house-number (Posted on 2013-06-04)
William lives in a street with house-numbers 8 up to 100. Lisa wants to know at which number William lives.
```She asks him: "Is your number larger than 50?"
Upon this, Lisa says: "I know your number if you tell me whether the first digit is a 3."
William answers, but now we don't know whether he lies or speaks the truth.```
Thereupon, Lisa says at which number she thinks William lives, but (of course) she is wrong.

What is William's real house-number?

 No Solution Yet Submitted by K Sengupta No Rating

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 a d1 answer Comment 3 of 3 |
81.
It had to be a square number, since Lisa hesitated between 2 possible choices.
The two sets under 50 and 50+ were  (9,16,25,36,49) and(64,81,100).
Lisa considered a wrong pair (16,36) while,being led  astray by wrong answers, missed a number which is over 50 and is not a multiple of 4.
WILLIAM's  3 answers were  no,yes,yes and Lisa's choice was either 36 (yes for the "3" digit ) or 16()case of "no").

Edited on June 4, 2013, 1:30 pm
 Posted by Ady TZIDON on 2013-06-04 13:05:03

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