Mathematics Problem Of the Week

Fall 2007

POW #10

Who Planted the Virus?

Someone put a virus in the CS networking lab last night. Six students had access to the lab and each visited once for some period of time during the night and then left. The Director of the lab, Dr. Hardcore, interviewed each of the students and asked who else they saw in the lab while they were working. The responses are summarized below.

Student	Andrea	Brett	Chris	Dan	Erin	Fred
Saw	Brett	Andrea	Andrea	Chris	Brett	Erin
	Dan	Chris	Fred	Fred	Dan	Dan

Since students may be engrossed in their work and not see or remember everyone who was also in the lab, Dr. Hardcore makes the following two assumptions

(a) If two students were in the lab at the same time, at least one of them remembers seeing the other.

(b) All students tell the truth, except the one who is guilty of dropping the virus in the network. That person will make up the name of someone who actually was not in the lab at the same time in order to try to deflect attention to that person.

Who planted the virus in the network? Explain your reasoning. You may get partial credit for identifying any student you know is innocent.

Due Friday, November 16^th at Noon.

Solutions should be submitted to Dr. R. Lock's mailbox in the Math/CS/Stat office or sent via e-mail to rlock@stlawu.edu.