Every friday, Bob is given a class test. The teacher doesn't check the students' answers by himself because there are 96 students in the class and he has other classes to manage as well. Instead, the teacher distributes those answer copies to other students in the same class such that no student gets his own copy. The teacher has a list according to which he distributes the copies. For example, Phineas always gets the copy of Ferb. And Ferb always gets the copy of Isabella. None of the students know who gets whose copy. That is, neither Phineas knows that he is checking the copy of Ferb, nor does Ferb know that his copy is being checked by Phineas. However, it seems like someone is having fun with Bob because Bob gets deducted marks even if his answers are correct.

How can Bob find out about the classmate who checks his copy every time, without letting the teacher know about it?

Some things to remember:

  • I took 96 arbitrarily.

  • I am not asking who. I am asking how can he find out about the classmate?

  • Isabella, Phineas and Ferb are just for examples. You can ignore them.

  • Just in case you think that I am Bob then I would say nope. This question just came to my mind accidentally.

  • 2
    $\begingroup$ Please give any three answers if you are voting to close it as too broad. $\endgroup$
    – manshu
    Commented Mar 4, 2016 at 17:11
  • 8
    $\begingroup$ Dust his paper with anthrax and see who dies. $\endgroup$ Commented Mar 4, 2016 at 17:53
  • $\begingroup$ @MackTuesday: that's mean! Dust his paper with dust and see who starts sneezing! :-) $\endgroup$ Commented May 4, 2016 at 2:08

3 Answers 3


He can

Write his answers upside-down, and watch to see who turns the paper in order to read. Whoever does will be invited to have a "strident discussion of proper grading procedure" with Bob after school.

  • $\begingroup$ I think this is perfect answer...it contains lot less troubles than the others... $\endgroup$
    – manshu
    Commented Mar 4, 2016 at 18:37
  • 1
    $\begingroup$ I fail to see how this would work. The person who corrects Bob’s copy doesn’t care about the answer. Whether or not they can read upside-down text doesn’t matter: they mark every question as false anyway. $\endgroup$
    – Édouard
    Commented May 3, 2016 at 17:03

There might be many legit ways to find out who marks Bob's paper but here's 2:

1) Paint the paper top red (or shed a corner, or any altering to the paper to make it outstanding to Bob but unnoticeable to the teacher)
2) Submit an empty test; Person who marks an empty test will instantly marks 0 and hand in the paper quickly

And I have to say, Bob = Manshu.

  • $\begingroup$ Deleted a duplicate post, thanks @Hellion $\endgroup$
    – Alex
    Commented Mar 4, 2016 at 20:06
  • $\begingroup$ should i hover on answer to see the content? $\endgroup$
    – Fast Snail
    Commented Mar 22, 2016 at 4:37
  • $\begingroup$ @FastSnail yes if you wish to see the answer, same for all other answers here $\endgroup$
    – Alex
    Commented Mar 22, 2016 at 14:32
  • $\begingroup$ interesting .is it standard for this site? in stackoverflow we don't do this [even i never know it's possible to hide a answer] $\endgroup$
    – Fast Snail
    Commented Mar 22, 2016 at 14:35
  • $\begingroup$ @FastSnail yea an interesting format esp for puzzle beta. Put >! in front of a line when you answer and it'll be hidden $\endgroup$
    – Alex
    Commented Mar 22, 2016 at 14:46

Possible answer:

He could put his name in an answer and threaten the person. Then wait for the day after grading and see who's avoiding him and keeping an eye out for him.


He could say give me an A and I'll pay you $100 and see who comes to claim it.

  • 1
    $\begingroup$ For first, I would say that you can't threaten the classmate who is sure that Bob doesn't know him. Another thing, the classmate will find out the he gets the copy of Bob. For second (which applies for the first too), I would say that the classmate can report it to the teacher in personal coz the restriction is on Bob, not on the classmate. $\endgroup$
    – manshu
    Commented Mar 4, 2016 at 17:24

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