Brain Teasers
Boxes of Notes
One day in the middle of the term, Leong was told to collect some lecture notes from the photocopy lady for his and the other four classes. The lecture notes were neatly stacked in boxes, with the number of lecture notes written on the box and the class written on a label pasted outside. On the way back to the classroom, a strong gust of wind blew the labels off the boxes.
If all five classes have different number of students, and there are no extra lecture notes in each box, what is the probability of Leong relabelling at least one of the boxes correctly?
If all five classes have different number of students, and there are no extra lecture notes in each box, what is the probability of Leong relabelling at least one of the boxes correctly?
Answer
100%. Leong's class is receiving one of the boxes of lecture notes, and as Leong would definitely know how many pupils are registered in his class, he can relabel the box belonging to his class correctly. No matter how, he will at least relabel one box correctly.Hide Answer Show Answer
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Comments
That was too simple. I figured it out in 10 seconds. Literally.
The answer isn't necessarily right - what if Leong didn't pay attention to how many students were in his class?
What is there to pay attention? It's not as if it is at the beginning of a new year. Unless you are really really really switched off in class, after time you will know what is the class enrolment.
I don't see how he would know how many people are in his lecture. Lecturers don't call roll and it's not a requirement to even show up, so how is he going to know the enrollment numbers? Anyway, the answer states that he would *definitely* know how many people are in his class, by the middle of term, and I just don't see how this is the case. Plus, it doesn't say how big the class is - it might have been a lecture of around 100 - so how is he going to know whether it's 100 or 101 people?
It says a CLASS. A class is different from a lecture. A lecture may have hundreds of people, but a class usually have 40 or less people. It may be a little misleading, putting the words class and lecture together, but after all, this is in the trick catergory.
Also, it is not stated what level of education Leong is studying at. At levels like U, there are lectures but no classes. At college or even secondary level, there are classes which are small in size and attendence is taken daily and also lecture groups which are large in size. They are two different things.
Hmmmm, I've always thought of the word "class" as a general term that means "a group of people gathering, often on a regular basis, to learn", while lectures, tutorials, workshops, and so on, are different forms of classes.
Anyway, my point is that the answer pretty much hinges on the fact that he would "definitely" know the numbers in his class, I'm not doubting the possibility, just the certainty, given the indefinite nature of the wording of the question
But hey, you got it, and I didn't, so what do I know, right?
Anyway, my point is that the answer pretty much hinges on the fact that he would "definitely" know the numbers in his class, I'm not doubting the possibility, just the certainty, given the indefinite nature of the wording of the question
But hey, you got it, and I didn't, so what do I know, right?
Maybe I was just switched off in class
I never know how many students are in the classes I'm in... Leong must have too much time on his hands, but it was a good teaser !
i have never known how many people were in my class,plus there are like 7 diff classes it would be almost imppossible to know how many were in the class for a certain one,u should have said he was a really smart geek or sometin
Not really. I only said he knows the number of people in HIS class. I never say he knows how many pupils there are in the other classes. And number of classes doesn't mean number of subjects or lessons.
Huh??? I'm sorry but i don't get it at all.
hmm... interesting.
cool!
I answered zero because he wasn't asked to put the labels back on and it therefore wasn't his responsibility to put the labels back on
I don't see how he would "definitely" know how many people were in his class but I reckon it would be quite easy to decide which boxes were the lightest or the heaviest.
i don't think he would know the exact number of people in his class, but still...
the term "photocopy lady" is a bit mean, though, don't you think? you could have just said "secretary".
the term "photocopy lady" is a bit mean, though, don't you think? you could have just said "secretary".
I guess this question really depends a bit on where you came from.
Just think of it like an elementry school. And unless you are from China or some similar places, there can't be too many pupils in one class.
And aball, here we just call photocopy shop or photocopy lady... Maybe I should have put shop instead of lady...
Just think of it like an elementry school. And unless you are from China or some similar places, there can't be too many pupils in one class.
And aball, here we just call photocopy shop or photocopy lady... Maybe I should have put shop instead of lady...
If you had used the word "you" (as in me) this teaser would have been dead wrong. Good thing you made up a name.
D'oh! You got me! I understand the explanation, and I don't disagree, but I for one never knew how many people were in my classes - 1st grade through college! But as long as there was somewhat of a difference in the number of students in each class, it should've been pretty easy for him to figure out. Nice teaser!
Why can't he open the box, glance at the class material inside and figure out the class names from that?
Opps, looks like I forgot to mention that the lecture notes topic was the same.
you made me really think but i got it
I dunno how likely it is that he will know exactly how many people there are in his class... But the chances are very high I guess. Especially if the labels have the number of sheets on them - he can surely count the sheets if he HAS to get one of them right?
i have 24 people in my class (the name of my class is prep d just (just throwing it in there))
nice teaser . but looking at it this way , at least 1 should mean probability of arranging 1 or 2 or 3 or 4 or 5 . of course the or is addition . if he can know everyon e in his class then he might just know people in another class . but then its a trick and it usually has many solutions
if the question was find the prob of arranging "any" of them the answer is definitely 100 percent
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