[b]p1.[/b] The number $100$ is written as a sum of distinct positive integers. Determine, with proof, the maximum number of terms that can occur in the sum.


[b]p2.[/b] Inside an equilateral triangle of side length $s$ are three mutually tangent circles of radius $1$, each one of which is also tangent to two sides of the triangle, as depicted below. Find $s$.
[img]https://cdn.artofproblemsolving.com/attachments/4/3/3b68d42e96717c83bd7fa64a2c3b0bf47301d4.png[/img]


[b]p3.[/b] Color a $4\times 7$ rectangle so that each of its $28$ unit squares is either red or green. Show that no matter how this is done, there will be two columns and two rows, so that the four squares occurring at the intersection of a selected row with a selected column all have the same color.


[b]p4.[/b] (a) Show that the $y$-intercept of the line through any two distinct points of the graph of $f(x) = x^2$ is $-1$ times the product of the $x$-coordinates of the two points.
(b) Find all real valued functions with the property that the $y$-intercept of the line through any two distinct points of its graph is $-1$ times the product of the $x$-coordinates. Prove that you have found all such functions and that all functions you have found have this property.


[b]p5.[/b] Let $n$ be a positive integer. We consider sets $A \subseteq \{1, 2,..., n\}$ with the property that the equation $x+y=z$ has no solution with $x\in A$, $y \in A$, $z \in A$.
(a) Show that there is a set $A$ as described above that contains $[(n + l)/2]$ members where $[x]$ denotes the largest integer less than or equal to $x$.
(b) Show that if $A$ has the property described above, then the number of members of $A$ is less than or equal to $[(n + l)/2]$.


PS. You should use hide for answers. Collected [url=https://artofproblemsolving.com/community/c5h2760506p24143309]here[/url].
1. We need to find the maximum number of distinct positive integers that sum to 100. Let's denote these integers as \(a_1, a_2, \ldots, a_k\) where \(a_1 < a_2 < \cdots < a_k\).
2. The sum of the first \(k\) positive integers is given by the formula:
   \[
   S_k = \frac{k(k+1)}{2}
   \]
3. We need to find the largest \(k\) such that:
   \[
   \frac{k(k+1)}{2} \leq 100
   \]
4. Solving the inequality:
   \[
   k(k+1) \leq 200
   \]
   This is a quadratic inequality. To solve it, we first solve the corresponding equation:
   \[
   k^2 + k - 200 = 0
   \]
5. Using the quadratic formula \(k = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\) where \(a = 1\), \(b = 1\), and \(c = -200\):
   \[
   k = \frac{-1 \pm \sqrt{1 + 800}}{2} = \frac{-1 \pm \sqrt{801}}{2}
   \]
6. Approximating \(\sqrt{801}\):
   \[
   \sqrt{801} \approx 28.3
   \]
   Thus:
   \[
   k = \frac{-1 + 28.3}{2} \approx 13.65
   \]
   Since \(k\) must be an integer, we take \(k = 13\).
7. Verify \(k = 13\):
   \[
   S_{13} = \frac{13 \cdot 14}{2} = 91
   \]
   This is less than 100.
8. Verify \(k = 14\):
   \[
   S_{14} = \frac{14 \cdot 15}{2} = 105
   \]
   This is greater than 100.
9. Therefore, the maximum number of distinct positive integers that sum to 100 is 13.

The final answer is \(\boxed{13}\).