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Freedonia has fifty senators. Each senator is either honest or corrupt. Suppose you know that at least one of the Freedonian senators is honest and that, given any two Freedonian senators, at least one is corrupt. Based on these facts, can you determine how many Freedonian senators are honest and how many are corrupt? If so, what is the answer?
in Mathematical Logic
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 @Deepak Poonia Sir, is my answer correct? Please check. 

We can right, "Suppose you know that at least one of the Freedonian senators is honest and that, given any two Freedonian senators, at least one is corrupt."

as "Suppose you know that given any two Freedonian senators, at least one of the Freedonian senators is honest and that at least one is corrupt."

then it means, a pair of senator like (s1, s2) follows Ex-or property for value honest and corrupt.So, s1 and s2 both can't be honest or corrupt. 

Now, as given in question "any two senators".So,we take a pair (s4, s9). 

Case1: Suppose, s4 is honest then s9 is corrupt. Like this you say that all senator except s4 are corrupt by pairing with s4. 

So, from case 1 we can conclude one senator is honest and 49 senators are corrupt. 

Case 2:Suppose, s4 is corrupt then s9 is honest. Like this you say that all senator except s4 are honest by pairing with s4. 

So, from case 2 we can conclude one senator is corrupt and 49 senators are honest. 

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edited by

You can’t conclude your statement based on the pair of s4 and s9..“given any two Freedonian senators” means pair of senators can be anything out of 50 senators, not only specific to s4 and s9.

Since, you have tagged the question as propositional logic, so going only this way.

Suppose there are $50$ senators as $S_1,S_2,….S_{50}$ and when we say $S_i$ is honest then assign the truth value of $S_i$ as True and when we say $S_i$ is corrupt then assign the truth value of $S_i$ as False for all $1 \leq i \leq 50.$

Now, we have two conditions:

  1. $S_ 1 \vee S_ 2 \vee S_ 3 \vee … \vee S_{50} \equiv T $
  2. $S_i \vee S_j \equiv F $ for all $1 \leq i,j \leq 50$          

Now for first condition to be hold, at least one $S_i$ should have a True as a truth value. Suppose, we have more than one $S_i$ as True then condition $2$ will not be hold because for those $S_i$ which have a True as truth value, if we take any two, say, $S_i$ and $S_j$ then $S_i \vee S_j \equiv T \vee T = T$ which contradicts the second condition and Hence, only one $S_i$ will be true and So, only one honest senator will be there and rest will be corrupt senators. 

Edit:  As mentioned by @pavan singh below, second condition will be $S_i \wedge S_j \equiv F $ for all $1 \leq i,j \leq 50$

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@ankitgupta.1729 i think there is one more constraints for second condition is (i $\neq$ j). 

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yes, you can add this for the clarity but “given any two Freedonian senators” implies that senators would be different unless you are making clone of the senators.
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@ankitgupta.1729 

as you say that,  $S_i \vee S_j \equiv T \vee T = T$

If $S_i = T$$,S_j=F$ then $T \vee F=T$ so, this also contradict with second condition. 

I think there is $\wedge$ instead of $ \vee$ in  second condition. 

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yes. you are right. Thanks.
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@Deepak Poonia One thing that I cannot follow in this question and the solutions written already, 

We can have 25pairs, each having honest-corrupt combination or some with corrupt-corrupt combination also. Then how to come to a conclusion?

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@chokostar Why only 25 pairs? We can have ${}^{50}C_2$ possible pairs right? 

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Why can we not have honest-corrupt pairings? In that case also, at least one corrupt and at least one senator being honest condition is satisfied!!

@gatecse

@tamal03

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I am not very confident with combinatorics yet, but 50C2 also seems correct now :(
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Is the following correct? 😉

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@chokostar This question is pretty simple actually and even combinatorics is not required. But it is very important because you get same kind of sentences in other subject questions like OS. See the highlighted parts below. 

given any two Freedonian senators, at least one is corrupt

Now, when we have 50 possible senators, the above condition can be true only when at least 49 of them are corrupt (pigeonhole principle). 50 being corrupt also satisfies the above condition but it is already given in the question that at least one is honest. 

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The question has mentioned about 50 senators not 50 pairs of senators.
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That was a typo – fixed now
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Chat GPT4 nailed it :)

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@gatecse Though GPT-4 has better accuracy than GPT-3 (GPT-3 had generated incorrect answer for question like this at that time while using multiple attempts)

But still GPT-4 has also some issues though I haven’t used much GPTs.

  1. What would be answer for this question according to GPT-4 ? Does it understand issue with these type of questions which are mentioned here 
  2. Does it add more creativity near to humans while solving questions like this (can check the structure of the given matrix whether it is upper triangular etc for computing eigen values or this (to add something for which it does not need a large value or use of calculator or involve much calculation) ).  
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@ankitgupta.1729 Here are the result for https://gateoverflow.in/391437/drdo-cse-2022-paper-2-question-24

To compute 3^{32} mod 80, we can first break down 80 into its prime factors as 80 = 2^4 * 5. Then, we can use the Chinese Remainder Theorem to compute the result.

First, we compute 3^{32} mod 2^4 and 3^{32} mod 5 separately:

  • 3^{32} mod 2^4:

We can use repeated squaring to compute this modulo. We start with 3^1 = 3, and then square it repeatedly:

3^2 = 9 3^4 = (3^2)^2 = 81 = 1 (mod 16) 3^8 = (3^4)^2 = 1 (mod 16) 3^16 = (3^8)^2 = 1 (mod 16) 3^32 = (3^16)^2 = 1 (mod 16)

Therefore, 3^{32} mod 16 = 1.

  • 3^{32} mod 5:

We can use Fermat's Little Theorem to compute this modulo, which states that if p is a prime and a is not divisible by p, then a^{p-1} = 1 (mod p). Since 5 is a prime and 3 is not divisible by 5, we have:

3^{4} = 81 = 1 (mod 5)

Therefore, 3^{32} = (3^4)^8 = 1^8 = 1 (mod 5).

Next, we use the Chinese Remainder Theorem to combine the results:

  • We need to find x such that x = 1 (mod 16) and x = 1 (mod 5).
  • Since 16 and 5 are coprime, we can use the formula:

x = apinv(p, q) + bqinv(q, p) (mod pq)

where p = 16, q = 5, a = 1, b = 1, inv(p, q) is the multiplicative inverse of p modulo q, and inv(q, p) is the multiplicative inverse of q modulo p. We can compute these inverses using the extended Euclidean algorithm:

  • inv(16, 5) = 1 (mod 5)
  • inv(5, 16) = 13 (mod 16)

Therefore,

x = 1161 + 1513 (mod 80) = 81 (mod 80)

Therefore, 3^{32} mod 80 = 81 mod 80 = 1.

 

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For eigen value it needed help

https://gateoverflow.in/400451/%23eigen-vectors

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To find the eigenvalues and eigenvectors of the given matrix using its upper triangular property, we can proceed as follows:

  1. The eigenvalues of an upper triangular matrix are simply its diagonal entries. Therefore, the eigenvalues of the given matrix are 1, 2, and 3.

  2. To find the eigenvectors, we need to solve the equation (A - λI)x = 0 for each eigenvalue λ. Here, I is the identity matrix of the same size as A. For example, to find the eigenvectors corresponding to the eigenvalue λ = 1, we need to solve the equation:

(A - λI)x = (1 - 1) x = 0

Substituting the values of A and λ, we get:

\begin{pmatrix} 1 & 0 & 1 \ 0 & 2 & 3 \ 0 & 0 & 3 \end{pmatrix} \begin{pmatrix} x_1 \ x_2 \ x_3 \end{pmatrix} = \begin{pmatrix} 0 \ 0 \ 0 \end{pmatrix}

Simplifying this equation, we get:

x1 + x3 = 0 2x2 + 3x3 = 0 3x3 = 0

From the last equation, we can see that x3 = 0. Substituting this value in the first equation, we get x1 = 0. Substituting x3 = 0 in the second equation, we get 2x2 = 0, which implies x2 = 0. Therefore, the eigenvectors corresponding to the eigenvalue λ = 1 are of the form:

x = \begin{pmatrix} 0 \ 0 \ 1 \end{pmatrix}t

where t is any non-zero scalar.

  1. Similarly, we can find the eigenvectors corresponding to the other eigenvalues λ = 2 and λ = 3. For λ = 2, we need to solve the equation:

(A - λI)x = \begin{pmatrix} -1 & 0 & 1 \ 0 & 0 & 3 \ 0 & 0 & 1 \end{pmatrix} \begin{pmatrix} x_1 \ x_2 \ x_3 \end{pmatrix} = \begin{pmatrix} 0 \ 0 \ 0 \end{pmatrix}

Simplifying this equation, we get:

-x1 + x3 = 0 3x2 = 0 x3 = 0

From the second equation, we can see that x2 = 0. Substituting this value in the first equation, we get x1 = x3. Therefore, the eigenvectors corresponding to the eigenvalue λ = 2 are of the form:

x = \begin{pmatrix} 1 \ 0 \ 1 \end{pmatrix}t

where t is any non-zero scalar.

  1. For λ = 3, we need to solve the equation:

(A - λI)x = \begin{pmatrix} -2 & 0 & 1 \ 0 & -1 & 3 \ 0 & 0 & 0 \end{pmatrix} \begin{pmatrix} x_1 \ x_2 \ x_3 \end{pmatrix} = \begin{pmatrix} 0 \ 0 \ 0 \end{pmatrix}

Simplifying this equation, we get:

-2x1 + x3 = 0 -x2 +

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And rubbish answer here.

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And rubbish answer here

 :p

@Arjun Sir, For $3^{32} \mod 80,$ Are you using GPT-3 and generating the response multiple times (Asking “Compute $3^{32} \mod 80$” multiple times (at least 2-3 times) to GPT) ? 

I have asked 4 times to compute $3^{32} \mod 80$ and 3 times it gives output as 71 and one time, it gives 21 as output. There are some memes also there to show lack of performance of ChatGPT-3 for some mathematical questions. 

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@ankitgupta.1729 I’m using GPT-4

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2 Answers

4 votes
4 votes
Suppose we assume that within those 50 person, A and B are honest and rest 48 are corrupt. Now in the question it is mentioned that whenever we take 2 person at least one of them is corrupted. Like it maybe possible that both are corrupted but there is no chance that both person are honest. So, when we will choose A and B it is not possible that both are honest because it is contradicting the question statement. It’s also mentioned that at least one person is honest.

So, it is clear that only 1 person is honest and rest 49 are corrupt.

4 Comments

Why can we not have honest-corrupt pairings? In that case also, at least one corrupt and at least one senator being honest condition is satisfied!!

@gatecse

@tamal03

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We can have exactly one H-C pair. If we have two such pairs say (H1, C1) and (H2, C2) that means (H1, H2) is also a possible pair and it violates the condition of “at least one corrupt in any pair”.
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Is it? What if we have 25pairs = 50 senators where every pair has one honest, one corrupt.

Which condition is violated here? (is what I am unable to understand)
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edited by
We have 50 senators and so we must consider ALL possible pairs out of them – there is no choice here. For each senator from $1..50$ he can be paired with any of the remaining senators. For the first senator he can be paired with any of the remaining $49$ senators. For the second senator he'll be having $48$ new senators to pair with and likewise the second last senator will have 1 new senator to pair with and the last senator will have 0 new senator to pair with. That’s how we get $49 + 48 + 47 + \ldots 1 + 0 = \frac{49.50}{2} = {}^{50}C_2$ possible pairs.
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Based on the given information, we can determine that at least one senator is honest, but we cannot determine the exact number of honest and corrupt senators.

We know that at least one senator is honest, but we do not know how many honest senators there are. It could be that only one senator is honest, or it could be that multiple senators are honest.

We also know that given any two Freedonian senators, at least one is corrupt. This means that if we choose any two senators, we know that at least one of them is corrupt. However, we cannot determine the number of corrupt senators based on this information alone. It could be that all but one senator is corrupt or that a majority or minority of the senators are corrupt.

Therefore, while we know that there is at least one honest senator and that given any two senators, at least one is corrupt, we cannot determine the exact number of honest and corrupt senators.

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