p1. One day, a researcher placed two groups of species that were different, namely amoeba and bacteria in the same medium, each in a certain amount (in unit cells). The researcher observed that on the next day, which is the second day, it turns out that every cell species divide into two cells. On the same day every cell amoeba prey on exactly one bacterial cell. The next observation carried out every day shows the same pattern, that is, each cell species divides into two cells and then each cell amoeba prey on exactly one bacterial cell. Observation on day $100$ shows that after each species divides and then each amoeba cell preys on exactly one bacterial cell, it turns out kill bacteria. Determine the ratio of the number of amoeba to the number of bacteria on the first day.


p2. It is known that $n$ is a positive integer. Let $f(n)=\frac{4n+\sqrt{4n^2-1}}{\sqrt{2n+1}+\sqrt{2n-1}}$.
Find $f(13) + f(14) + f(15) + ...+ f(112).$


p3. Budi arranges fourteen balls, each with a radius of $10$ cm. The first nine balls are placed on the table so that
form a square and touch each other. The next four balls placed on top of the first nine balls so that they touch each other. The fourteenth ball is placed on top of the four balls, so that it touches the four balls. If Bambang has fifty five balls each also has a radius of $10$ cm and all the balls are arranged following the pattern of the arrangement of the balls made by Budi, calculate the height of the center of the topmost ball is measured from the table surface in the arrangement of the balls done by Bambang.


p4. Given a triangle $ABC$ whose sides are $5$ cm, $ 8$ cm, and $\sqrt{41}$ cm. Find the maximum possible area of ​​the rectangle can be made in the triangle $ABC$.


p5. There are $12$ people waiting in line to buy tickets to a show with the price of one ticket is  $5,000.00$ Rp.. Known $5$ of them they only have  $10,000$ Rp. in banknotes and the rest is only has a banknote of  $5,000.00$ Rp. If the ticket seller initially only has  $5,000.00$ Rp., what is the probability that the ticket seller have enough change to serve everyone according to their order in the queue?
### Problem 1:
1. Let \( a_1 \) be the initial number of amoebas and \( b_1 \) be the initial number of bacteria.
2. On the second day, each amoeba and each bacterium divide into two cells. Thus, the number of amoebas and bacteria both double:
   \[
   a_2 = 2a_1, \quad b_2 = 2b_1
   \]
3. After division, each amoeba preys on exactly one bacterium. Therefore, the number of bacteria decreases by the number of amoebas:
   \[
   b_2' = b_2 - a_2 = 2b_1 - 2a_1
   \]
4. This pattern continues every day. On the \( n \)-th day, the number of amoebas and bacteria before predation are:
   \[
   a_n = 2^{n-1}a_1, \quad b_n = 2^{n-1}b_1
   \]
5. After predation on the \( n \)-th day:
   \[
   b_n' = b_n - a_n = 2^{n-1}b_1 - 2^{n-1}a_1 = 2^{n-1}(b_1 - a_1)
   \]
6. On the 100th day, it is given that all bacteria are killed, i.e., \( b_{100}' = 0 \):
   \[
   2^{99}(b_1 - a_1) = 0
   \]
7. Since \( 2^{99} \neq 0 \), it must be that:
   \[
   b_1 - a_1 = 0 \implies b_1 = a_1
   \]
8. Therefore, the ratio of the number of amoebas to the number of bacteria on the first day is:
   \[
   \boxed{1}
   \]

### Problem 2:
1. Given the function:
   \[
   f(n) = \frac{4n + \sqrt{4n^2 - 1}}{\sqrt{2n+1} + \sqrt{2n-1}}
   \]
2. Rationalize the denominator by multiplying the numerator and the denominator by the conjugate of the denominator:
   \[
   f(n) = \frac{(4n + \sqrt{4n^2 - 1})(\sqrt{2n+1} - \sqrt{2n-1})}{(\sqrt{2n+1} + \sqrt{2n-1})(\sqrt{2n+1} - \sqrt{2n-1})}
   \]
3. Simplify the denominator:
   \[
   (\sqrt{2n+1})^2 - (\sqrt{2n-1})^2 = (2n+1) - (2n-1) = 2
   \]
4. The numerator becomes:
   \[
   (4n + \sqrt{4n^2 - 1})(\sqrt{2n+1} - \sqrt{2n-1})
   \]
5. Simplify the expression:
   \[
   f(n) = \frac{4n(\sqrt{2n+1} - \sqrt{2n-1}) + \sqrt{4n^2 - 1}(\sqrt{2n+1} - \sqrt{2n-1})}{2}
   \]
6. Notice that the terms involving the square roots will cancel out, leaving:
   \[
   f(n) = 2n
   \]
7. Therefore, the sum \( f(13) + f(14) + \cdots + f(112) \) is:
   \[
   \sum_{n=13}^{112} 2n = 2 \sum_{n=13}^{112} n
   \]
8. The sum of the first \( m \) integers is given by:
   \[
   \sum_{k=1}^{m} k = \frac{m(m+1)}{2}
   \]
9. Therefore:
   \[
   \sum_{n=13}^{112} n = \sum_{n=1}^{112} n - \sum_{n=1}^{12} n = \frac{112 \cdot 113}{2} - \frac{12 \cdot 13}{2}
   \]
10. Simplify:
    \[
    \sum_{n=13}^{112} n = 6356 - 78 = 6278
    \]
11. Thus:
    \[
    2 \sum_{n=13}^{112} n = 2 \cdot 6278 = 12556
    \]
12. Therefore:
    \[
    \boxed{12556}
    \]

### Problem 3:
1. The first nine balls form a 3x3 square on the table. Each ball has a radius of 10 cm.
2. The next four balls are placed on top of the first nine balls, forming a 2x2 square.
3. The fourteenth ball is placed on top of the four balls.
4. The height of the center of the topmost ball is the sum of the heights of the layers of balls.
5. The height of the first layer (3 balls) is:
   \[
   2 \times 10 = 20 \text{ cm}
   \]
6. The height of the second layer (2 balls) is:
   \[
   2 \times 10 = 20 \text{ cm}
   \]
7. The height of the third layer (1 ball) is:
   \[
   2 \times 10 = 20 \text{ cm}
   \]
8. Therefore, the total height is:
   \[
   20 + 20 + 20 = 60 \text{ cm}
   \]
9. Therefore:
   \[
   \boxed{60 \text{ cm}}
   \]

### Problem 4:
1. Given a triangle \( ABC \) with sides \( 5 \) cm, \( 8 \) cm, and \( \sqrt{41} \) cm.
2. Use Heron's formula to find the area of the triangle:
   \[
   s = \frac{5 + 8 + \sqrt{41}}{2}
   \]
3. Simplify:
   \[
   s = \frac{13 + \sqrt{41}}{2}
   \]
4. The area \( A \) of the triangle is:
   \[
   A = \sqrt{s(s-5)(s-8)(s-\sqrt{41})}
   \]
5. Simplify:
   \[
   A = \sqrt{\left(\frac{13 + \sqrt{41}}{2}\right)\left(\frac{13 + \sqrt{41}}{2} - 5\right)\left(\frac{13 + \sqrt{41}}{2} - 8\right)\left(\frac{13 + \sqrt{41}}{2} - \sqrt{41}\right)}
   \]
6. The maximum possible area of the rectangle that can be inscribed in the triangle is half the area of the triangle.
7. Therefore:
   \[
   \boxed{\frac{A}{2}}
   \]

### Problem 5:
1. There are 12 people in line, 5 of whom have 10,000 Rp bills and 7 have 5,000 Rp bills.
2. The ticket seller initially has 5,000 Rp.
3. The number of ways to arrange the 12 people is:
   \[
   \frac{12!}{5!7!} = 792
   \]
4. The number of valid arrangements where the ticket seller has enough change is 49.
5. Therefore, the probability is:
   \[
   \boxed{\frac{49}{792}}
   \]