The Math Major

CSU Fresno Mathematics Department

Vol 1. No. 6

Editor: Dr. Larry Cusick.

Math Department Colloquium Schedule

The Math Department Colloquia are a series of talks intended for a general audience. Students, in particular, are encouraged to attend.

Spring Math Courses

The math department will offer 11 upper division and 4 graduate level mathematics courses this spring. In the last issue you saw descriptions of maths 101-161. Here are the rest.

Tutor Jobs

The CSUF/UC Davis Medi-Corp Program is now hiring math/science tutors for Junior High and High School students in the Fresno area. It pays $6-7 per hour for 10-12 hours per week (may work on Saturdays). If you are interested, pick up an application in the SCOP office Science 136 (278-4748).

Bounty Math

Math pays! The Bounty Math web page lists open mathematics problems whose posers offer cash awards for correct solutions. Awards range from $50 to $10,000. Here is a $1,000 offer from John H. Conway (inventor of the "Conway's Game of Life" and Princeton mathematics professor):

The Thrackle Problem ($1,000): Is there a graph drawn in the plane such that each edge is a straight or curvy line segment, every pair of edges makes either an X (crosses once) or a V (shares exactly one vertex) but not both, and which has more edges than vertices?

The Bounty Math web page lists about two dozen problems.


Problem Corner

Problem 1.5: A list of consecutive positive integers beginning with 1 is written on a black board. One of the numbers is erased. The average (arithmetic mean) of the remaining numbers is 35 7/17. What number was erased?

Solution to Problem 1.5: Suppose the original list is 1, 2, ..., n. If 1 were erased, the resulting average would be (n+2)/2, where as if n were erased, the average would have been n/2. This gives us the inequality: n/2 less than or equal to 35 7/17 less than or equal to (n+2)/2. Solving for n we see that n must be 69 or 70. Since 35 7/17 is the average of n-1 integers, (35 7/17)(n-1) must be an integer. Thus n = 69. Let x be the number erased. Then x must satisfy ((1/2) (69)(70) - x)/68 = 35 7/17 from which we can solve for x = 7.

Correct solutions to problem 1.5 were received Anar Ahmeov, Bryan Sheldon, Patrick Villa and David Yoshihara.

New Problem

Problem 1.6 The sides of a triangle are proportional (all with the same proportionality constant) to the roots of the cubic equation x^3 - a x^2 + b x - c = 0. Find the sum of the cosines of the angles of the triangle.

Solutions may be delivered to the math department office (for Dr. Cusick) or by e-mail at larry_cusick@csufresno.edu. no later than Thursday November 7, 3pm. There is a $75 dollar first prize and a $50 second prize to be awarded at the end of the semester to the student(s) who submit the most correct solutions.


CSU Fresno Math Department Home Page

California State University, Fresno