I am an honest person, and am thinking of one of three numbers: 1, 2 or 3. You may ask me EXACTLY one yes-no question, I will answer truthfully, and if you chose the right question, you will know which number I’m thinking of!
Communicated by Rob Andler.
Hint: you need to find a question which, even though one is trying to get the other person to say yes or no, is such that sometimes neither yes nor no is appropriate. If this doesn’t help, email me at [email protected].
Is the number 2 smaller than the number you are thinking of?
You’re on the right track. If the number is 3 you would answer no; however, if the number is 1 or 2 you would answer no.
Is the number you’re thinking of greater than 1 but smaller than 3?
The problem with this is that if the number is 1 you say no, but if it is 2 or 3 you say yes and thus you cannot distinguish b/w 2 and 3.
If the number was three you would answer ‘no’; if the number was two you would answer ‘yes’, but if the number is one you would also answer ‘no’ as that number is NOT greater than one.
I don’t think this works. You say yes if it is 3, but you say no if it is 2 or 1.
If you subtract 2 from your number, is the result positive?
not quite — I’d answer ‘no’ if my number were 1 or 2, as 0 is not positive.
The answer I came up with a long time ago, when I solved this problem was, “I’m thinking of 2 numbers. One of them is 1. The other is either 2 or 9. Is the number you’re thinking of one of the numbers I’m thinking of?”
Is the number you’re thinking of larger than 1 and smaller than 3?
I prefer not to post the solns online, as that ruins the fun for some people as they might accidentally see the answer before they’re ready to see it. Email me at [email protected] for the soln. .s
Soo many ideas so few answers. Lets go with. Will you tell me your number?
I don’t see how this will work. If the person says ‘no’ then you’re stuck.
mukuro: correct! not posting as it’s the answer.
If i was to subtract one from the number you chose how many positive numbers would I have to choose from? If it is 1 the answer would be 1. If it was 2 the answer would be none and if it was 3 the answer would be 2.
This isn’t a yes/no qusetion; this is just a question with three answer.
Johnny: correct: not posting as it’s the soln. Well done. /s
To whomever posted with f(x) — not quite sure if that works, as (x-3)/(x-3) is often replaced with 1.
okay,
so if you take your number and take away 1, then divide your number by the number that is one less that it, is the answer an even number?
to awesome: I think you’re on the right track but there are some grammar mistakes and your answer isn’t clear. Email me at [email protected]….
not quite == 1 and 3 are both non-even primes, so you’d say no for both.
1 isn’t a prime. Prime numbers are numbers divisible by 1 and itself. So it has 2 factors. But 1 is a number with only 1 factor and isn’t considered a prime. If the answer was no then the answer would be 3; 2 if the answer was yes. Am I right?
correct. As 1 is not a prime, it cannot be an even prime. As 3 is odd, it cannot be an even prime. Thus, your question has two NO answers (1 and 3) and only one YES answer (2).
witch of your answers(yes or no) has the number of letters that it is the number you are thinking of? that way, if it’s one, he cant answer it
I dont’ think this works — email me at sjm1 AT williams.edu to chat more.
more please — divided by 2 what? email me at sjm1 AT williams.edu
Convert 1,2,3 into 1 cat, 2 dogs and 3 cats. Ask the question “Are you thinking of more than one cat? Yes means 3, No means 1, silence means 2.
but why can’t I say “no” if I’m thinking of 2 dogs. If I’m thinking of 2 dogs, I’m not thinking of more than 1 cat.
I would ask: If you subtract 2 from the # that you are thinking, is the solution positive or negative?
This isn’t a yes/no question: try to rephrase and send to me at sjm1 AT williams.edu
if they answer no then it’s 1 or 3 but you don’t know which
Ask “Is the number a factor of 4856423”. If they are thinking of 1 they will say yes cos one goes into everything, if they are thinking of two they will say no cos the number is odd, if they are thinking of three they will either say i dont know or will take a long time to work it out.
doesn’t matter if it takes a long time — they can figure it out. actually, isn’t too bad. 3 divides the number if and only if it dividesthe sum of digits. doesn’t divide.
Written by Steven Miller on April 12, 2011.Reply
Hint: you need to find a question which, even though one is trying to get the other person to say yes or no, is such that sometimes neither yes nor no is appropriate.
I saw you wrote this, so I was trying to ask a question that was a (yes or no) but still neither (yes or no) is appropriate.
Is the number 2 smaller than the number your thing of, but grater than 1??
email me (sjm1 AT williams.edu) how this works. If it’s 3, 2, or 1 what do you get?
doesn’t work as 1 is a unit and not prime, so if the number is 1 or 2 you answer no. email me at [email protected] to discuss more //s
sergio: love the phrasing, one of the best I’ve seen; email me at sjm1 AT williams.edu if you want to chat more.
Lukas: correct! you can email me at sjm1 AT williams.edu
yoav: email me at sjm1 AT williams.edu for solns / discussions
that doesn’t work -=- 1 is considered a unit and not prime (sjm1 AT willilams.edu)
Is the number two above it odd and the number two below it positive?
this sadly doesn’t work:: 1 and 2 are both ‘no’s’ — sjm1 AT williams.edu
I have an even better answer than my previous:
Is the square root of the number two below your number odd? (If n=your number, is sqrt(n-2) odd?)
This doesn’t work — sqrt(0) and sqrt(-1) are both no’s (sjm1 AT williams.edu)
I don’t see why this works — sjm1 AT williams.edu
very easy
is your number 1? (Yes)
is your number 2? (No)
is your number 3? (No)
But you only have ONE question (sjm1 AT williams.edu)
Jim Sansone: email to you bounced. Your answer to 1,2,3 is one of the best I’ve seen. .s ([email protected])
o: meow meow ima cat ([email protected]): Please email me at [email protected] to discuss your soln.
If you want a response to your comments you must leave a valid email address. Failure to leave a valid email address may result in your post being ignored. The reason is all posts are moderated to make sure nothing is posted that will give away the solution to someone who does not wish to see it.
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