## Problem of the Day #216: Red Lines Blue Lines
*October 21, 2011*

*Posted by Saketh in : potd , add a comment*

Alex takes a set of $N$ points and draws either a red line or a blue line between each pair. What is the smallest $N$ such that he will always create a closed path consisting of four segments, all of the same color?

## Problem of the Day #215: Sharing Some Apples
*October 20, 2011*

*Posted by Saketh in : potd , add a comment*

Sam recently bought some apples, $4$ for each of his friends. He is trying to divide them as evenly as possible. If none of his apples weighs more than $k$ times any other, determine the smallest value $r$ for which he can guarantee that no group weighs more than $r$ times any other. Express $r$ in terms of $k$.

## Problem of the Day #214: Albert’s Number Line
*October 19, 2011*

*Posted by Saketh in : potd , add a comment*

Albert has arranged the numbers from $1$ to $N$ in a line such that the sum of any two adjacent numbers is a perfect square. What is the greatest $N$ for which this is possible?

## Problem of the Day #213: Length of an Angle Bisector
*October 18, 2011*

*Posted by Saketh in : potd , add a comment*

Triangle $ABC$ has sides of length $39$, $48$, and $71$. The bisector of angle $A$ cuts $BC$ at point $D$. Find the length of $AD$ in terms of $cos(\frac{A}{2})$.

## Problem of the Day #212: Number of Distinct Qualifying Sets
*October 17, 2011*

*Posted by Saketh in : potd , add a comment*

Alex is picking certain subsets of the set $\{1,2,3,…,50\}$. To qualify, a set must have a sum of at least $777$. Determine the number of distinct sets from which Alex can choose.

## Problem of the Day #211: A Pig Stuck inside Its Pen
*October 16, 2011*

*Posted by Alex in : potd , add a comment*

Albert the Pig is chained by a stiff leash, of length $x$, to one of the corners of a pen, in the shape of a regular hexagon with side length $1$. Albert must stay within the pen. The leash does not bend but Albert’s neck allows him to reach areas up to $0.1$ units beyond his leash. Find $x$ such that the area of land that Albert can reach is maximized.

## Problem of the Day #210: Albert’s Sequence
*October 15, 2011*

*Posted by Billy in : potd , add a comment*

Albert has a sequence defined by \[\begin{align*}a_0 &= a_1 = a_2 = 0 \\ a_3 &= 1 \\ a_n &= 3 a_{n-2} - a_{n-4}.\end{align*}\] Find $a_{31}$.

## Problem of the Day #209: Maximum Possible Inradius
*October 14, 2011*

*Posted by Alex in : potd , add a comment*

Find the largest possible inradius of a quadrilateral with side lengths $4$, $5$, $6$, and $7$.

## Problem of the Day #208: Binary Coins
*October 13, 2011*

*Posted by Alex in : potd , add a comment*

Saketh wants to purchase some food worth a random value of cents between $0$ and $1,000,000$, inclusive. He has coins worth $1$ cent, $2$ cents, $4$ cents, and so on to infinite powers of $2$, with an infinite number of coins for each value. What is the expected number of coins that Saketh will use to purchase his food, given that he always uses the fewest possible number of coins?

## Problem of the Day #207: Points on a Plane
*October 12, 2011*

*Posted by Saketh in : potd , add a comment*

Four points are arranged on a plane such that the distance between every pair is either $a$ or $b$. If $b>a$, find all possible values of $\frac{b}{a}$.