The puzzle asks players to work out a maths question to ensure all students in a teacher's class receive a prize at the end of the school year for all their hard work(Image: Getty)

Only those with high IQ can solve baffling brainteaser set in school classroom

by · Irish Mirror

People have been left scratching their heads over a baffling brainteaser aimed to reveal whether you have a high IQ or not. The puzzle asks players to work out a maths question to ensure all students in a teacher's class receive a prize at the end of the school year for all their hard work.

Shared on Reddit, it reads: "A teacher has an advance maths class containing 7 students. Every class for the whole year ends with the teacher putting a random number from 1-7 on their heads (they can have the same number as someone else in the class, everyone could get a 5 for example).

"The students are allowed to look at each others numbers, but not communicate. They then have to guess what number is on their head. As long as at least 1 student guesses correctly every class, they will be taken out for pizza at the end of the year.

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"All the students love pizza, especially well earned pizza, so what strategy can they employ to guarantee they get it? Their guess is to be written down, and the teacher takes it from their desk." While most users tried and failed to work out the correct answer, others asked for clues to help them come up with a solution.

What is the toughest brainteaser you know of?
byu/DarthRiven inAskReddit

One user asked: "Are the students allowed to not guess? Would the other students see the prior students not guessing?" While someone else added: "I don't understand how this is possible, the numbers are independent from each other and no communication is allowed. So looking at the other students' numbers wouldn't give you any information on your number."

A third user said: "Would there be no other form of communication either? So could you say all students completely blind, deaf, no sense of time, nothing and only get the information of the other students number by Morse code tipping on their hand?

"I have a solution when they are able to see the others writing, not what they write in any way but in which order they are writing. Like if the sum of the 6 other numbers is even, student A starts writing, if not he waits etc." Providing a hint, the original poster said: "With just 2 classmates this would be easy enough (and the numbers only 1 or 2).

"If student A writes down the number on student B's head, and student B writes down the number not on student A's head, one of them will correctly guess the number on their own head."

Sharing the correct answer, a final user said: "The nth student assumes that the sum of all the numbers is n modulo 7. Since he knows the numbers on everyone else's head, he can work out his own number using that. Now if the sum is m modolu 7, then the mth student's assumption was correct, so he managed to work out his own number correctly. Success! Note that:

  1. We have 7 students which is exactly enough to cover all possibilities mod 7.
  2. Everyone else's assumption was wrong so they all had incorrect answers. That doesn't matter since we only needed one person to have the right answer."

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