# Question about finding correct exam answers..

#### Mathhelp98

##### New member
Hello so their in my country exam consists of thrre subjects math , Verbal, English... The maximum score u can get in this exam is 800 , it's very hard to get 800 , i think less than 100 got 800 in the last 20 years ... So i know i guy who solved this question with one equation.. u must choose 1 answer from 4 , and for each subject their 3 chapters each chapter is 20 questions.. so what this guy did is , he solved the first 20 questions from the first chapter and successed to create algebra equation with one X(question number) variable and y (correct answer 4) , that X is the number of the question u want answer for it and when u do put the question number in X it gives you Y the correct answer!!
Im really amazed how he did such a thing, any clues?
Example
Y=x+2
y= 5(question number) -1
y= 4
The correct answer from 1-4 answers is the forth...

#### tkhunny

##### Moderator
Staff member
I'm sorry, but we'll need two things.
1) A MUCH better translation, and
2) A MUCH better description of the problem.

#### Dr.Peterson

##### Elite Member
So i know i guy who solved this question with one equation.. u must choose 1 answer from 4 , and for each subject their 3 chapters each chapter is 20 questions.. so what this guy did is , he solved the first 20 questions from the first chapter and successed to create algebra equation with one X(question number) variable and y (correct answer 4) , that X is the number of the question u want answer for it and when u do put the question number in X it gives you Y the correct answer!!
Im really amazed how he did such a thing, any clues?
Example
Y=x+2
y= 5(question number) -1
y= 4
The correct answer from 1-4 answers is the forth...
As I understand it, your friend took the answers to the first 20 questions, all of which are numbers from 1 to 4, and wrote an expression (function) that gives those values. For example, if the answer to question #5 is 4, then his function gives f(5) = 4.

There is a standard method for finding a polynomial function for a (finite) sequence of numbers; in fact, the last question I just answered dealt with the same method. Here is one of the links I gave him: Method of Finite Differences. Here is another: The Method of Common Differences.

Typically, with 20 random values, the formula you get will be a polynomial with degree 19, and the coefficients will be horrible numbers; with luck, it might be nicer.

Does this sound like what you are asking about?

#### Mathhelp98

##### New member
As I understand it, your friend took the answers to the first 20 questions, all of which are numbers from 1 to 4, and wrote an expression (function) that gives those values. For example, if the answer to question #5 is 4, then his function gives f(5) = 4.

There is a standard method for finding a polynomial function for a (finite) sequence of numbers; in fact, the last question I just answered dealt with the same method. Here is one of the links I gave him: Method of Finite Differences. Here is another: The Method of Common Differences.

Typically, with 20 random values, the formula you get will be a polynomial with degree 19, and the coefficients will be horrible numbers; with luck, it might be nicer.

Does this sound like what you are asking about?
Yeah something like that , but u know when he get the function so he can solve all the exam with this fuction , chapter 1,2,3..etc

#### stapel

##### Super Moderator
Staff member
Yeah something like that , but u know when he get the function so he can solve all the exam with this fuction , chapter 1,2,3..etc
There is no "formula" that gives the answers to all questions. I mean, all the instructor would have to do is re-order the questions, and the "function" would fail. In other words, the above makes no sense.

Please reply with a better translation of whatever is actually going on. Thank you! 