William lives in a street with house-numbers 8 up to and including 100. Lisa wants to know at which - Note that Lisa does not know that William sometimes lies. Lisa reasons as if William speaks the truth. Because Lisa says after her third question, that she knows his number if he tells her whether the first digit is a 3, we can conclude that after her first three questions, Lisa still needs to choose between two numbers, one of which starts with a 3. A number that starts with a 3, must in this case be smaller than 50, so William's (lied) answer to Lisa's first question was "No". Now there are four possibilities: nummer is a multiple of 4 : (16, 36 number is a square) : 8, 12, 20, and more nummer is not a square nummer is not a multiple of 4 : (9, 25, 49 number is a square) : 10, 11, 13, and more nummer is not a square Only the combination "number is a multiple of 4" and "number is a square" results in two numbers, of which one starts with a 3. William's (lied) answer to Lisa's second question therefore was "Yes", and William's (true) answer to Lisa's third question was also "Yes". In reality, William's number is larger than 50, not a multiple of 4, and a square. Of the squares larger than 50 and at most 100 (these are 64, 81, and 100), this only holds for 81. Conclusion: William's real house-number is 81. - Logical & Aptitude Interview Questions and Answers

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Question: William lives in a street with house-numbers 8 up to and including 100. Lisa wants to know at which number William lives. She asks him: "Is your number larger than 50?" William answers, but lies. Upon this Lisa asks: "Is your number a multiple of 4?" William answers, but lies again. Then Lisa asks: "Is your number a square?" William answers truthfully. 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 Williams real house-number?

Answer: Note that Lisa does not know that William sometimes lies. Lisa reasons as if William speaks the truth. Because Lisa says after her third question, that she knows his number if he tells her whether the first digit is a 3, we can conclude that after her first three questions, Lisa still needs to choose between two numbers, one of which starts with a 3. A number that starts with a 3, must in this case be smaller than 50, so William's (lied) answer to Lisa's first question was "No". Now there are four possibilities: nummer is a multiple of 4 : (16, 36 number is a square) : 8, 12, 20, and more nummer is not a square nummer is not a multiple of 4 : (9, 25, 49 number is a square) : 10, 11, 13, and more nummer is not a square Only the combination "number is a multiple of 4" and "number is a square" results in two numbers, of which one starts with a 3. William's (lied) answer to Lisa's second question therefore was "Yes", and William's (true) answer to Lisa's third question was also "Yes". In reality, William's number is larger than 50, not a multiple of 4, and a square. Of the squares larger than 50 and at most 100 (these are 64, 81, and 100), this only holds for 81. Conclusion: William's real house-number is 81.

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Question: William lives in a street with house-numbers 8 up to and including 100. Lisa wants to know at which number William lives. She asks him: "Is your number larger than 50?" William answers, but lies. Upon this Lisa asks: "Is your number a multiple of 4?" William answers, but lies again. Then Lisa asks: "Is your number a square?" William answers truthfully. 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 Williams real house-number?

Answer:

Note that Lisa does not know that William sometimes lies. Lisa reasons as if William speaks the truth. Because Lisa says after her third question, that she knows his number if he tells her whether the first digit is a 3, we can conclude that after her first three questions, Lisa still needs to choose between two numbers, one of which starts with a 3. A number that starts with a 3, must in this case be smaller than 50, so William's (lied) answer to Lisa's first question was "No". Now there are four possibilities: nummer is a multiple of 4 : (16, 36 number is a square) : 8, 12, 20, and more nummer is not a square nummer is not a multiple of 4 : (9, 25, 49 number is a square) : 10, 11, 13, and more nummer is not a square Only the combination "number is a multiple of 4" and "number is a square" results in two numbers, of which one starts with a 3. William's (lied) answer to Lisa's second question therefore was "Yes", and William's (true) answer to Lisa's third question was also "Yes". In reality, William's number is larger than 50, not a multiple of 4, and a square. Of the squares larger than 50 and at most 100 (these are 64, 81, and 100), this only holds for 81. Conclusion: William's real house-number is 81. Source: CoolInterview.com

81

Since Lisa guess was "3.", that mean the range what william lied is Less than 50 range. But the very truth is that the Range is above 50.

When lisa asked william about the 2nd and 3rd questions, boths answers must be +ve otherwise Lisa would have lots of guesses. But the Lisa answer was precise and this could be only possible when answer to 2nd & 3rd question is +ve, i.e "YES". (Lisa guess was "36".) Out of which william lied on 2nd question.

Compendium of the facts :

> William house is no is more than 50

> William house is not divisible by 4

> William house is square of any number

House number 81 satisfies all the aforesaid requirements Source: CoolInterview.com

Answered by: Raj | Date: 4/13/2010 |

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