p1. From the measurement of the height of nine trees obtained data as following.
a) There are three different measurement results (in meters)
b) All data are positive numbers
c) Mean$ =$ median $=$ mode $= 3$
d) The sum of the squares of all data is $87.$
Determine all possible heights of the nine trees.


p2. If $x$ and $y$ are integers, find the number of pairs $(x,y)$ that satisfy $|x|+|y|\le 50$.


p3. The plane figure $ABCD$ on the side is a trapezoid with $AB$ parallel to $CD$.  Points $E$ and $F$ lie on $CD$ so that $AD$ is parallel to $BE$ and $AF$ is parallel to $BC$. Point $H$ is the intersection of $AF$ with $BE$ and point $G$ is the intersection of $AC$ with $BE$. If the length of $AB$ is $4$ cm and the length of $CD$ is $10$ cm, calculate the ratio of the area of ​​the triangle $AGH$ to the area of ​​the trapezoid $ABCD$.
[img]https://cdn.artofproblemsolving.com/attachments/c/7/e751fa791bce62f091024932c73672a518a240.png[/img]


p4. A prospective doctor is required to intern in a hospital for five days in July $2011$. 
The hospital leadership gave the following rules:
a) Internships may not be conducted on two consecutive days.
b) The fifth day of internship can only be done after four days counted since the fourth day of internship. Suppose the fourth day of internship is the date $20$, then the fifth day of internship can only be carried out at least the date $24$.
Determine the many possible schedule options for the prospective doctor.


p5. Consider the following sequences of natural numbers: 
$5$, $55$, $555$, $5555$, $55555$, $...$ ,$\underbrace{\hbox{5555...555555...}}_{\hbox{n\,\,numbers}}$ .
The above sequence has a rule: the $n$th term consists of $n$ numbers (digits) $5$.
Show that any of the terms of the sequence is divisible by $2011$.
To determine the number of possible schedule options for the prospective doctor, we need to find the number of integer solutions to the following constraints:

1. Internships may not be conducted on two consecutive days.
2. The fifth day of internship can only be done after four days counted since the fourth day of internship.

Let's denote the days of internship as \(d_1, d_2, d_3, d_4, d_5\) where \(d_1 < d_2 < d_3 < d_4 < d_5\). 

Given the constraints:
- \(d_{i+1} \geq d_i + 2\) for \(i = 1, 2, 3, 4\) (no consecutive days)
- \(d_5 \geq d_4 + 4\) (fifth day at least four days after the fourth day)

We can transform these constraints into a simpler form by defining new variables:
\[ x_1 = d_1 - 1 \]
\[ x_2 = d_2 - d_1 - 1 \]
\[ x_3 = d_3 - d_2 - 1 \]
\[ x_4 = d_4 - d_3 - 1 \]
\[ x_5 = d_5 - d_4 - 4 \]

These transformations ensure that \(x_i \geq 0\) for all \(i\). The total number of days in July is 31, so we have:
\[ d_5 \leq 31 \]

Substituting the transformations into the total days constraint:
\[ (d_1 - 1) + (d_2 - d_1 - 1) + (d_3 - d_2 - 1) + (d_4 - d_3 - 1) + (d_5 - d_4 - 4) + 1 + 1 + 1 + 1 + 4 = 31 \]
\[ x_1 + x_2 + x_3 + x_4 + x_5 + 10 = 31 \]
\[ x_1 + x_2 + x_3 + x_4 + x_5 = 21 \]

We need to find the number of non-negative integer solutions to the equation:
\[ x_1 + x_2 + x_3 + x_4 + x_5 = 21 \]

This is a classic "stars and bars" problem in combinatorics. The number of non-negative integer solutions is given by:
\[ \binom{21 + 5 - 1}{5 - 1} = \binom{25}{4} \]

Calculating the binomial coefficient:
\[ \binom{25}{4} = \frac{25!}{4!(25-4)!} = \frac{25!}{4! \cdot 21!} \]
\[ = \frac{25 \times 24 \times 23 \times 22}{4 \times 3 \times 2 \times 1} \]
\[ = \frac{25 \times 24 \times 23 \times 22}{24} \]
\[ = 25 \times 23 \times 22 \]
\[ = 12650 \]

The final answer is \( \boxed{12650} \).