﻿ No surprise puzzle

# No surprise puzzle

## No logic, no war - A no surprise puzzle

The attack cannot take place on day-7. If 6 days have passed without an attack, the great leader will know for sure, (therefore it is no longer a surprise) that day-7, the last day, will be the day.

The attack cannot take place on day-6. If 5 days have passed without an attack, the great leader will know for sure, (therefore it is no longer a surprise) that day-6, will be the day, because we have logically concluded that a surprise attack cannot take place on day-7

The attack cannot take place on day-5. If 4 days have passed without an attack, the great leader will know for sure, (therefore it is no longer a surprise) that day-5, will be the day, because we have logically concluded that a surprise attack cannot take place on days 7 and 6.

The attack cannot take place on day-4. If 3 days have passed without an attack, the great leader will know for sure, (therefore it is no longer a surprise) that day-4, will be the day, because we have logically concluded that a surprise attack cannot take place on days 7, 6 and 5.

The attack cannot take place on day-3. If 2 days have passed without an attack, the great leader will know for sure, (therefore it is no longer a surprise) that day-3, will be the day, because we have logically concluded that a surprise attack cannot take place on days 7, 6, 5, and 4.

The attack cannot take place on day-2. If day-1 have passed without an attack, the great leader will know for sure, (therefore it is no longer a surprise) that day-2, will be the day, because we have logically concluded that a surprise attack cannot take place on days 7, 6, 5, 4 and 3.

The attack cannot take place on day-1. The great leader will know for sure, (therefore it is no longer a surprise) that day-1, will be the day, because we have logically concluded that a surprise attack cannot take place on days 7, 6, 5, 4, 3 and 2.

It is indeed logically impossible to launch a surprise attack if the enemy has been told that the attack date will happen within 7 days following the detonation.

If George W. Bush could only stick to the "Bush doctrine", we wouldn't have to deal with this silly logic yawn.

## A surprise quiz puzzle

The setup is as follows:
Friday afternoon, just before school lets out, a teacher promises his class that they will have a quiz on one of the five days of the coming week. Moreover, he guarantees the students that the quiz will be a surprise in that they won't be able to predict the night before that it will happen the next day.

The class is dismayed until one of the students realizes that something fishy is going on.

She reasons: "The quiz can't be given on Friday, for sure, because that's the last possible day, so we would be able to predict it Thursday night. So Friday is out. That makes Thursday the last possible day the quiz can be given. But then the quiz also can't be given on Thursday, because Wednesday night we would know it was coming the next day! And in the same way we can eliminate Wednesday, Tuesday, and even Monday from the list of possible days for the quiz."

This argument is good enough to convince the rest of the class, who gleefully go about their business, content in the certainty that there can be no surprise quiz.

Tuesday morning comes, however, and the teacher hands out a quiz sheet to each student.

There are, of course, objections: "You can't give this quiz! We already figured out that you couldn't make it a surprise no matter what day you gave it on!"
But the teacher is unperturbed. "You figured that out, did you? Well, here's the quiz. Aren't you surprised?"
The students reluctantly agreed that they were.
But where did their logic go awry?

This is the excerpt in precise words from the source: www.math.cornell.edu Adam Bjorndahl (page 18)
Similar puzzle can also be seen at ?