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Past Problems

2008
61 (May 7) 60 (Mar 26) 59 (Feb 15) 58 (Jan 25)
2007
57 (Nov 20) 56 (Oct 19) 55 (Sep 21) 54 (May 11)
53 (Apr 20) 52 (Apr 4) 51 (Mar 13) 50 (Feb 21)
2006
49 (Dec 5) 48 (Nov 14) 47 (Oct 30) 46 (Oct 9)
45 (Sep 19) 44 (Apr 28) 43 (Apr 7) 42 (Mar 20)
41 (Feb 15)
2005
40 (Dec 11) 39 (Nov 11) 38 (Oct 27) 37 (Oct 5)
36 (Sep 16) 35 (May 18) 34 (Apr 29) 33 (Apr 8)
32 (Mar 9) 31 (Feb 11)
2004
30 (Dec 15) 29 (Nov 22) 28 (Nov 3) 27 (Oct 13)
26 (Sep 24) 25 (May 3) 24 (Apr 16) 23 (Mar 24)
22 (Feb 25)
2003
21 (Dec 10) 20 (Nov 14) 19 (Oct 22) 18 (Oct 1)
17 (May 5) 16 (Apr 25) 15 (Mar 28) 14 (Mar 7)
13 (Feb 7)
2002
12 (Dec 20) 11 (Dec 2) 10 (Nov 11) 9 (Oct 21)
8 (Oct 4) 7 (Sep 18) 6 (May 8) 5 (Apr 22)
4 (Mar 27) 3 (Mar 11) 2 (Feb 20) 1 (Feb 6)

Problems in 2008



Problem Number 61

May 7, 2008

Winners:

We call an integer *lucky* if it is a sum of positive integers (not necessarily distinct) whose reciprocals sum to 1. For example, 4 and 11 are lucky: 4=2+2, 1/2 + 1/2 = 1, and 11=2+3+6, 1/2 + 1/3 + 1/6=1. However, 2, 3, and 5 are unlucky. Find all unlucky numbers.


Problem Number 60

March 26, 2008

Winners:
(undergraduate) Donald Adams
Lamia Mekha
Marzhel Pinto
Marco Fernandez
Spencer Williams
(graduate) Renee Thompson
Vince Dayes

Solve the equation (ln x)^2 - 2.5(ln x)(ln(4x-5)) + (ln (4x-5))^2 = 0,
where x and all expressions are real.


Problem Number 59

February 15, 2008

Winners: (graduate) Vince Dayes

Fibonacci Nim is a two player game, played as follows. Players
take turns removing stones from a pile (and discarding the removed stones).
They must remove at least one stone, but no more than twice what their opponent
removed immediately before. Whoever removes the last stone(s) wins, and the
first player may remove any number of stones (except all of them).


Here's a sample game, starting with 10 stones:

A removes 2, leaving 8

B may remove between 1 and 4, chooses to remove 1, leaving 7

A may remove either 1 or 2, chooses to remove 1, leaving 6

B may remove either 1 or 2, chooses to remove 2, leaving 4

A may remove between 1 and 4, chooses to remove 4, A wins.


You are playing with your friend, starting with 40 stones. Your friend went
first, and removed nine (which was a mistake). There are now 31 stones. What
is the only move you can make, to guarantee victory?


Problem Number 58

January 25, 2008

Winners:
(undergraduate) Al Sison III
Robbie Chasse
Jon David
Jonathan Saavedra
Philip Tabares
Tony Tam
Parisa Tarani
(graduate) Emiliano Vega
Vince Dayes

Six chess knights are on a 3x3 board, as pictured.
Find a sequence of legal chess knight moves that end up with the diagram reversed,
(i.e. the black knights on the bottom and the white knights on the top).

Three by three chess board. Top row has three black knights, bottom row has three white knights, middle row is empty.
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