Posted by M.A. on Tuesday, February 9, 2010 at 9:45am.
Four students fall asleep during class and, while asleep, the professor rearranges their notebooks so that when they wake up, nobody has his or her own notebook. In how many ways could the professor have rearranged the notebooks?
4
6
9
24
Explain

math  drwls, Tuesday, February 9, 2010 at 11:31am
The correct answer is nine.
Student A can get any of three books: b, c or d. Assume he gets b. Then there are only three possibilities of distributing the remaining three (a, c and d) among students B, C and D. B can get a, c or d, but there is only one way to distribute the other two. The same logic applies to each of the three possible assignments to student A.
3 x 3 = 9

math  Dawn, Tuesday, February 9, 2010 at 11:34am
hey how come u didn't mind giving the correct answer this time drwls????

math (for Dawn)  drwls, Tuesday, February 9, 2010 at 1:05pm
The hardest part of the problem for me was figuring out a method of solution. My first attempt, using factorial numbers, was wrong. So I took more time to think about it, and even made a list of possible rearragements. Computing the number was easy, once the logic was done properly.
Students who are only looking for a number to plug into a computerized test sheet are missing the fun of mathematics, and will probably never master the subject.

math  bobpursley, Tuesday, February 9, 2010 at 1:06pm
Let the students be abcd
and the exams ABCD
Here are the possible ways to distribute exams:
BCDA
BDAC
BADC
CADC
CDAB
CDBA
DABC
DCAB
DCBA
Answer This Question
Related Questions
 Math  Four students fall asleep during class and, while asleep, the professor ...
 math  A store sells small notebooks for $8 and large notebooks for $10. If you ...
 algebra  You are buying two kinds of notebooks for school. A threering ...
 math  11 notebooks were added to w notebooks. 7 friends then shared the ...
 math  1. What is the experimental probability that the next customer buys any ...
 math  an airline passanger fell asleep halfway to her destination. When she ...
 Math  The school store opened on the first day of scroll with 56 notebook and ...
 Math  The school store opened on the first day of scroll with 56 notebook and ...
 sdu  . A man finds that two things cause him to wake up at nightnoise or ...
 Math  At Bob's binders, a set of 3 notebooks costs $4.20. At Pam's Paper Place ...
More Related Questions