Challenging Math Problems (Or not)

[zyzzyva980]

Hmm... finally one I may be able to figure out. Let me think about it.

[lllazar]

Here's one that tripped me up for a few days:

Find the next number in the sequence and the solution

53

You subtract the second digit of the number from the first digit, and then subtract this from the whole number to get the next number in the sequence.

Yes, that is a possible solution and i thought of that too but it wouldn't work for all sequences of this kind. Can you find the other way to do it? Hint: 9.

[SOninja]

"You are trapped in a prison and the guard decides to play a game. If you win, you will be allowed to leave. But if you lose, you die. The guard says that he is thinking of number 1, number 2, or number 3. You are allowed to ask one question to find out which of these three numbers the guard has in mind. However, the guard will only answer with a “yes”, “no”, or “I don’t know”. What should you say to the guard?"

uhhh :/ i'll venture a guess

random guess (Click to Show Hidden Text)

"is the number either even or prime?"

[winneratlife]

"You are trapped in a prison and the guard decides to play a game. If you win, you will be allowed to leave. But if you lose, you die. The guard says that he is thinking of number 1, number 2, or number 3. You are allowed to ask one question to find out which of these three numbers the guard has in mind. However, the guard will only answer with a “yes”, “no”, or “I don’t know”. What should you say to the guard?"

uhhh :/ i'll venture a guess

random guess (Click to Show Hidden Text)

"is the number either even or prime?"

Won't work, cuz he will only answer "yes" or "no"

The answer to that would have to be like "yes but no"

[paleonaps]

I think this is it-

Answer (Click to Show Hidden Text)

"Is the number prime, my dear fellow?"

[winneratlife]

I think this is it-

Answer (Click to Show Hidden Text)

"Is the number prime, my dear fellow?"

And if he says yes?

[RandomPerson]

uhhh :/ i'll venture a guess

random guess (Click to Show Hidden Text)

"is the number either even or prime?"

He can only answer "yes", "no" or "I don't know". You can't ask that question.

There are 3 possible numbers, and 3 possible responses. A correct answer (there are many) will have these three responses differentiate between the three. Getting "Yes" and "No" is easy, its the "I don't know" which becomes difficult.

I think this is it-

Answer (Click to Show Hidden Text)

"Is the number prime, my dear fellow?"

Yes -> 2 or 3
No -> 1

If you get Yes, You can't be sure if it is 2 or 3 and risk getting killed. This is incorrect.

[lllazar]

I think this is it-

Answer (Click to Show Hidden Text)

"Is the number prime, my dear fellow?"

And if he says yes?

Ya, wat comes after the yes, if he does say yes. It could be 2 or 3.

[paleonaps]

You then divide by zero, so that this happens:

[winneratlife]

uhhh :/ i'll venture a guess

random guess (Click to Show Hidden Text)

"is the number either even or prime?"

He can only answer "yes", "no" or "I don't know". You can't ask that question.

There are 3 possible numbers, and 3 possible responses. A correct answer (there are many) will have these three responses differentiate between the three. Getting "Yes" and "No" is easy, its the "I don't know" which becomes difficult

Given that the guard knows all about math, doesn't this make it impossible? That was my first thought.

I'm going to assume that the "I don't know" fits with 1 though...